And despite all that, he was basically ousted from the school he supposedly had so much control over, for what again? Saying “Wizard Hitler bad, and maybe not actually dead, and we should probably consider doing something about that”? Seems like a fairly uncontroversial proposition, and yet look at the results.

Do you really think that highlighting the slavery supporting wizard society would have been better received? How many of the pure blood families would have left that move unchallenged? How many of his friends in high places would have backed him up? How much of that influence and political capital would he have used up just getting legislation drafted, much less passed?

You don’t maintain influence by calling in favors frivolously, and there are bigger fish to fry than house elves. Wizard Hitler, for example.