one of my favourite things to think about regarding izuku is whether or not he's oblivious to his feelings for katsuki. and when i say feelings, i mean just that--feelings. not necessarily romantic.
as i dive deeper into his character, i'm coming to this conclusion:
he is not oblivious to the fact that he has complicated and undefined feelings for katsuki. those feelings and his reactions to said feelings are shameful, "gross" according to izuku.
but his behavior, inspired by katsuki, is instinctual now.
he's talking to toga like he doesn't understand how someone could do awful things in the name of love, yet he shames himself for just insulting villains. on a lesser scale, izuku knows that feeling of wanting to be like someone else but being shamed for it--even if he himself is the one doing the shaming.
that's why he's significantly less empathetic towards himiko. he can understand shigaraki and touya. he tried to understand muscular, but resolved to just defeat him.
he doesn't give himiko that same empathy. because he relates to her and it hurts him.
