Not a clue. This ain't really a phenomenon that started with Voldemort, either. Some of these same families were doing the same thing with Grindelwald. Guess the best I can say is that it aligns with their goals and keeps 'em in power, and dark magic makes 'em soulless.
That's not really an answer for you, but I've bloody seen happen to some people you wouldn't guess. [...] Cause that whole thing about Albus being friends with Grindelwald? It's true.