No vidya is inherently good or bad. It's their mode and purpose of use that makes them good and bad. For example, engineers read chemistry and create explosives to destroy mountain and create highways for the benefit of people. But then some other kind of people study them and create explosives to hurt humans. So just like guns which can be used to either defend oneself or kill another, so also tantra or any other kind of vidya can be used in both ways.
But because it is primarily helpful to people it's there in the Atharva veda and still exists in the world. But the thing is that, due to the ill effects of this age of kali, knowledge which were once used for the benefit and well being of the people are now being used for hurting them. It is because most of those occult practitioners are narrow minded, uneducated and of tamas nature [BG - 17.5,6].
Now regarding whether it hurts the users who hurt others, the answer is yes. Everything is karma, those practitioners know this well. Doesn't matter who or what you are, you can never escape from the effects of your karma. So if someone uses it for bad purpose, then eventually the bad effects will catch him sooner or later. That is why most of these practitioners' life and death are terrible. Worshiping and revering ghosts, in the end they too become ghosts themselves [BG - 9.25]. Like you I had also heard about these from some old people and read stories in some local books. I answered your question on that basis.
