Decide what you want in Mentalists. Suppose you had a large number of low-grade mentalists who could not affect people's minds, but could pick up minds in the area, superficially but enough to detect such malice as assassination. As long as the assassin didn't teleport exactly where needed and away again, he could be defended against.
The details of what superpowers you put in a world would do a lot to determine what the world would end up like.
I suspect the very biggest difference would be Mentalists who could tell whether people were telling the truth. Imagine how many trials, both civil and criminal, that would simplify.