Are there any real-life parallels to the Night's Watch and their fall from prestige?

Question

In A Song of Ice and Fire (and also in the series Game of Thrones), the Night's Watch is a peculiar institution: Regardless of its actual usefulness, it serves a supposedly "vital" function which was originally considered an honorable endeavor by all cultures which partook in the tradition. In other words, the Night's Watch was considered a vital and beneficial institution, and joining the watch was considered a very honorable thing to do. Over time, however, the practical function of the Night's Watch changed from "guarding the realms of men" to being a last resort for criminals, the disinherited and the disgraced. Over time, it gained a stigma among most people, but this stigma failed to gain much traction in one place — namely, in the North. Likewise, although the Watch is pretty much considered by Southerners to serve only as an alternative to death and/or (even greater) disgrace, it seems that some Northerners still willingly join (such as Benjen Stark did).

Visualizing the practical function of the Night's Watch for respective regions compared to their perception of the Night's Watch in a table suggests that the perception of the Night's Watch is correlated with the function of it over time: As all the non-Northern kingdoms used the Watch for ever less-reputable reasons, it begins to be perceived as less reputable as well... but this trend doesn't hold with Northern culture(s) as far as the books seem to portray it/them (albeit that nearly all information provided is from the point of view of noblemen rather than the common folk):

        | The North                           | Elsewhere                   |
        |-------------------------------------|-----------------------------|
Era     | Function               | Perception | Function     | Perception   |
--------| -----------------------|------------|--------------|--------------| 
Earlier | Reputable              | Reputable  | Reputable    | Reputable    |
Later   | Reputable/disreputable | Reputable  | Disreputable | Disreputable |

It strikes me as very much... fantasy that such a well-established tradition can exist and "degrade" so much and yet be "tolerated" for so long while one significant group remains an "outlier" in still valuing it. However, G.R.R. Martin takes liberal inspiration from history, so it may be possible that the Night's Watch was inspired by some parts of real-world history... knowingly or otherwise. So, are/were there any real-life institutions/orders/traditions which originally served a highly-respected function to everyone but became stigmatized over time to everyone except for a certain subculture and yet continued to exist for a long time^†?

The only (very weak) parallel I can think of is that of monastic orders such as the Benedictines, but it doesn't fit very well because they're not stigmatized but simply entail a career path and lifestyle that not many aspire to following these days. Is there any institution in real-world history which has gone from holding an esteemed function in society to being heavily stigmatized and its function degraded... and yet continued to exist for so long?

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^†Since everything in A Song of Ice and Fire seems to last for ridiculously long periods of time, the scope of what constitutes a "long time" would of course have to be adjusted for the real world.

Answer 1

The French Foreign Legion A.K.A. "Légion étrangère" or FFL have some similarities: it is a military branch of french army established in 1831 based on volunteering of foreign people.

Similarities:

• Based on volunteering
• Patchwork of different cultures: Both have soldiers coming from different cultures
• Strong team spirit: related to previous point, a strong team spirit is here to ensure that despite culture diferences, the organisation is united and strong
• NW have their vows while FFL have their code of honour
• Independence: As NW is independent from Seven Kingdom's, despite fighting for it, FFL does not swear allegiance to France
• Useless army still here for traditional reasons: As you say, NW serves a supposedly "vital" function that have no sense (after all, the Other is just a myth, isn't it ?), the original function of FFL was primarily used to protect and expand the French colonial empire. Today, France no longer have any colonial empire, but the FFL is still here
• Shattered reputation: AS NW, the FFL reputation suffer a lot by the fact that anyone could engage, including criminals who wanted to start a new life.
• Even if it's not 8000 years old, one could argue that an almost bicentenary army corp is quite old for our world, as the NW is for Westeros
• There are some evidence that FFL == NW: See this picture of Zombie Jon with skin coming off his cheek, With FFL in French Guiana (Circa 282 AC, Colorized)
  _{(credits to @Aegon for this wonderfull photomontage totally real picture)}

There are however some differences:

• the FFL is a place to improve one's standing and has continual high standards of quality in what it does even if the thing it was originally meant for isn't needed anymore

  (credits to @errantlinuist)

• the FFL is a dead-serious military force, and its reputation as a place for disgraced men seems to be fading. The FFL is not a place for incompetent soldiers or a place to fool around. It can provide a second chance in some circumstances, and is a well-known way to lawfully immigrate to the EU (Legionnaires qualify for French citizenship after a few years)

  (credits to @RobertColumbia)

• FFL is not an until-death contract, you are totally free once your contract is over, and you can even acquire french citizenship

Answer 2

Roman Legions

One of George R. R. Martin's main inspirations for the Night's Watch are the Roman Legions who manned Hadrian's Wall, as that is the inspiration for the Wall.

Hadrian's Wall, of course, I think was the inspiration for the Wall. I've never been to China so I've never had a chance to see their Great Wall but I have been to Scotland and I have walked along what remains of Hadrian's Wall and that was actually an inspiring experience. I was travelling and we got there late, all of the tour busses were leaving, the sun was going down and so we pretty well had it to ourselves. I remember standing along that wall and it was Fall, it was late October or early November and the wind was picking up and I looked across trying to think what it would be like to be a Roman legionary, maybe someone from Italy or Sicily or Greece who was posted to this place and what would be likely to come out of those hills to attack him there on the wall, what he must have felt, it was a very kind of lonely feeling. And I've always held onto that and certainly it was a feeling I tried to tap into when I created the Wall and the men of the Night’s Watch.
But of course, the other thing about fantasy is [that it is] bigger than real life, so you don't just take Hadrian's Wall and write something, you have to have something bigger than Hadrian's Wall. Hadrian's Wall is like, I don't know, 20 feet tall, if that, 10 feet tall, and my wall is like 700 feet tall and built of ice and it's much more impressive. I think that's true of all the castles. There are no real life castles that can match the castles of Westeros. That being said, they are still modest compared to some of the things in Lord of the Rings, and Tolkien's castles. Then again, there is less magic in my world, so it would be harder to build.
_{So Spake Martin, Second Life Appearance}

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As with most writers George takes inspiration from his real life and has commented on the Wall/Night's Watch being inspired from his experiences during the 1967 Chicago Blizzard.

One young woman asked Martin if the frozen far North of his fantasy world was anything like Chicago winters.
"The coldest winter was in Chicago, let me tell you about cold," Martin said of his freshman year at Medill. He leaned forward.
"There was so much snow that winter, you couldn't see, all snow, all ice, and it was so very cold," Martin said.
The old storyteller stared her in the eyes and made a whooshing motion with his hands, conjuring Chicago wind and ice, and I could see the frozen drifts of the Wall begin to grow.
It was the great Chicago blizzard of 1967 he was talking about. Some 23 inches of snow fell in one 48-hour period, and when it was all done, the Chicago area was paralyzed.
There were mountains of snow and 10-foot drifts. People had carved out little pathways in the snow, and as more snow fell, the walls of snow began to grow as tall as a tall man. Then they grew taller still, and the snow walls froze into solid ice.
"It was like the trenches during World War I, but they were trenches of ice," Martin said. "I remember walking through the trenches and the tunnels of ice, the wind blowing so you couldn't even see. It's an experience that never left me."
Martin said he supposed that was where the Wall began in his mind, years later, when he began to write "Ice and Fire."
_{Chicago Tribune, Chicago's blizzard of 1967 and its connection to 'Game of Thrones'}

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On a side note though George doesn't like to have a one to one mapping of his stories/characters/places to any historical event. There are some characters who are mainly inspired by one person but then have a twist in to change them a bit but no one appears to be a direct comparison. With that in mind it's likely that the Night's Watch is a combination of different real world examples.

I don't like to just take a character from history, whoever it is, and just change his name, kind of file off the serial number and present him as my own character. What I much prefer to do is perhaps take 2 or 3 characters from history and mix them up together or do juxtapositions that are original; I mean I don't want…I love historical fiction as a reader, but one of the problems with historical fiction, if you read a lot of history, you're always going to know how it's comes out. If you read a novel that’s actually set during the Wars of the Roses, you know what’s going to happen to those two little boys in the tower; you know who's going to win the Battle of Bosworth Fields. You know the ultimate fate of the mad King Henry VI. So I don't like that, I don’t want someone to just look at my book and know what happens because they're recognizing historical analogues, I like the stories to be unpredictable.
_{So Spake Martin, Second Life Appearance}

Answer 3

And I will add to the pot the various orders of knights during the crusades, most notably the Knights Hospitaller. They were a well regarded bunch when they formed in 1099, and were repeatedly given land as the fortunes of war changed in the Middle East. They were considered a vital check on the expansion of Islamic power in this period.

They moved to Malta in the 1530 and their reputation dwindled through the next several hundred years, with the northern states being increasingly hostile as the reformation took hold. Then they were seriously persecuted after Napoleon took Malta in 1798, and were accused of all sorts of heinous acts.

Then reformed again in the 1800s as a charitable organization and remain to this day, although in various semi-related groups.

Answer 4

Although the Nights Watch was a more "noble" cause to fight for in ASOIAF, when I first read it I felt as though Martin had taken inspiration from the German WWII "Strafbattalion", a military penal unit formed by Hitler as a way to keep troublemakers and malcontents away from the regular military units. They were used for jobs that nobody wanted, or for "lost cause" campaigns where their loss was insignificant to the greater war efforts, especially early on when the Germans were winning. As the war started going bad, they refilled the ranks with civilian criminal prisoners and their tasks became almost suicidal, such as clearing mine fields. So in a way, they were "lifetime" assignments, because very few of them survived the war.

Answer 5

This is pretty different from all of the other examples, but I thought I would throw this out here: The Aztec practice of human sacrifice. While the majority of adults sacrifices are thought to have been warriors captured in battle, the children sacrificed are thought to have been primarily noble children offered up by their parents. All in all a noble institution, right? Well, at least for a while.

Human sacrifice wasn't unknown to the other, neighboring religions, so it was largely tolerated.

The Aztecs had a habit of increasing sacrifices during tough times, though, and things got really bad for them a few years before Europeans arrived in Mexico. The Aztecs ramped up the sacrifices, eventually turning their neighbors against the practice. By the time Cortez showed up, many tribes were in full-on revolt due to the intense increase in sacrifices (which, of course, were almost exclusively coming from commoners of unfavored tribes at this point), and the Spanish were able to play both sides of the Civil War against each other.

The Aztecs, of course, saw these sacrifices as necessary, but all their neighbors changed their perception of the institution in a hurry.