I think people vastly overestimate Edwin as a person. We know he's capable of some truly heinous shit by the choices available to him. I wouldn't call him a psychopath, but he's definitely fucked in the head more than average.
I mean, the first time we see him, he's sitting there naked watching his mom get gangbanged, debating on his own morality. I'm pretty sure he already knows he's not all good in the head.
There's also his unhealthy obsession with his mother, where he assigns little to no agency to her and twists himself into pretzels to make her a martyr for doing porn, because the only way he can justify it to himself is thinking she endured it all for him, even though he clearly has a huge problem with it he refuses to think about. He's also a shut in loner, and even Victoria herself is worried about him.
He also spends an alarming amount of time thinking about his mom taking dick, especially while he's having sex. He can also have sex with his "best friend's" ex girlfriend, he can manipulate said friend at the behest of his mother, he can cheat on his actual girlfriend, he can take advantage of Rose's situation to make her his sex slave etc.
My point is, Edwin's not a good guy. And given how dissasociated he is, especially at the beginning, it's not that far fetched to think Kat drugging him doesn't bother him much, especially since he got to roughhouse a bunch of helpless house girls.