Laws will differ based on the country you happen to be in.
Here in the UK where I live, as of November 2015, we don’t require a permit to shoot non commercial photos in public areas.
Currently, the Police in the UK do not have powers to stop you from taking photos in public areas.
As there are currently no general privacy laws in the UK, people are free to take images of other people, however, as photographers, a gentle acknowledgment such as a smile, goes some way to receiving little to no objection. Most people even smile back or hit a pose!
However, if someone does ask for their image to be deleted, then the photographer should take into account the European Convention on Human Rights and perhaps delete the image in order to respect the rights for the other persons privacy. Saying that, the photographer is not under legal obligation to delete an image if the place where the image was taken, the subject did not have a reasonable expectation of privacy. This also applies to children where a parent may ask for the image to be deleted, as it is not currently an illegal offence to take a decent image of a child in a public place and remains the discretion of both parties whether the image should be deleted or not.
This general policy covers people, street performers, random kids and painters and artists selling their work. As long as they are on public land with no real expectations of privacy, then you can take the image and only delete if you wish to respect the European Convention on Human Rights.
Regarding private property; you may be on a public street, however, if you happen to be standing in front of a building where the front pavement also happens to be owned by that building, then you are not allowed to take an image without prior authority as it is private land. If you refuse to leave, then that can be seen as trespassing and security can use reasonable force to remove you.
This includes most of the fields and farmland of the UK as they are pretty much all privately owned. However, you can shoot an image where the scene is made up of the farmers land, as long as you are on a public road! Similarly, the same rule applies to taking images of interiors from a public road. You can do that and only delete if you are confronted and wish to do so. Once again, if the people inside the building do not have a reasonable expectation of privacy, they cannot force you to delete the image.
In the UK, certain government buildings and all airports have bylaws which can restrict any person from being a certain distance from a perimeter fence and these bylaws are quite often sign posted. However, besides Parliament Square and Trafalgar Square, both of which have slightly tighter rules, you can take images of airports or government buildings from public areas.
It is also okay to take photos on public transport such as Trains and Underground Tube Network but there are restrictions such as no Flash and Tripod.
Finally, in the UK we do have stop and search Policies.
Up till March 2011 the police could stop you under section 44 of the Terrorism Act 2000 which required no suspicion of an offence, and you would have to surrender your camera for inspection. Since then, this has been changed to Section 47a where the stopping officer, "reasonably suspects that an act of terrorism will take place”, and reasonably considers that the authorisation “is necessary to prevent such an act”.
Under section 43, terrorism Act 2000, where if there is reasonable doubt to suspect you, the camera can taken off you and viewed. If there is cause and reason to suspect you further, the camera can be seized. If you have taken images of a policeman or a member of armed forces, you can be arrested.
Finally, morality, well I guess that is subjective to the photographer.