Didn't they try to do that with Enterprise?
Buffy has hella double standards when it comes to morality. Xander tries to magically force a woman to love him it's fun Xander hijinks. Warren does it it's appropriately labeled rape.
The show easily let Xander off the hook for what he attempted to do to Cordelia and ended up doing to everyone else, but take away the fact that Warren's spell on Katrina ended in murder, it's pretty much the exact same thing.
One could also make an argument that Willow committed rape when she made Tara forget the fight.
But it's okay when a main character does it, apparently.
Not to defend Xander too much, because he was entirely wrong and stupid and the episode definitely could've used some more long-term consequences, but it's not the same thing Warren did. Xander wanted to make Cordelia fall in love with him so he could break up with her. It's cruel and vindictive and manipulative and not ok, but it's not rape.