Voldemort was the good guy in Harry Potter. The unforgivable hexes were fine and even Harry Potter realizes it by the end such that he started casting a couple. I doubt blacks on average would be able to cast the unforgivable curses because of the skill involved in them. Most wizards were incapable of casting them. It's estimated that only 5% of the wizarding world could cast them, that means pretty much 100% of blacks would be unable to cast them.

No, 13% of wizards would be responsible for 52% of crimes but they wouldn't involve the unforgivable hexes. Only the Nazis of the wizarding world were mostly capable of them becsuse if their superior genetics.