Well, technically, they aren't exactly the same thing. Yet again, technically, more than just one term from the list can be applied to a person at the same time. There even have been precedents in history that show that. And the main point is, all the three terms denoting the social models mean something most of the people would normally avoid living in.
So, it's natural that they get generalized into one term meaning what ppl in general try to keep away from. (including but not limited to, of course)