I feel like half the comments are acting like the story endorses this guy's behaviour
A story doesn't usually give this much attention to some random antagonist. If they get a background story expounded like this, chances are it's indeed meant to "redeeming" in some sense. That's not saying it's endorsing what he's doing, but it's certainly saying "there's something there".
Worst recent case I remember is some fantasy adventure manga where some princess committed genocide against the heroine's people and the reader very clearly was meant to forgive her because daddy treated her badly and she knows better now ...
... obviously, this is not comparable; but a disconnect between an author "I like this character" and the audience "I hate them" and the story development thus not feeling satisfying is not exactly uncommon.