LadyLavinia
Scooby
Nobody said the action itself should be condoned, it's more about whether or not the motives behind it are understandable. It's not all black and white; even a judge in court will make a difference in their sentence according to the motive. If you steal something to feed your starving kid, you're quite likely to get a milder punishment than if you do it just for kicks... even though both thefts are illegal and will result in some kind of judicial consequence. (And I hope you agree that it's a good thing that such differentiation is done!)
Angel never had a real motive to erase Buffy's memories. It was unecessary. Frankly, I suspect that he didn't want to face her reaction to his need to resume being a vampire. His returning to his vampire state did nothing to help Buffy, except when he gave her that amulet in the second to last episode of BUFFY. That's it. Angel really has no justification for the mind rape.
It's amazing. Fans have condemned Willow for her acts of psychic rape in BUFFY's early Season 6. They have condemned Spike for his attempted rape of Buffy. But Angel, on the other hand, has received nothing but tea and sympathy from many fans because of the "glorification" of the Buffy/Angel relationship. Jesus!