I agree with you, and in the same time, I don't. which is why in my opinion nobody wanted to share their ideas.
not interacting with someone drunk is to protect the drunk person from doing something he/she wouldn't have done in normal situation: they don't love you, but they have revenge sex with you because they were disappointed with their lover (that's why they drunk), and obviously, they will regret it afterwards. in this situation, ok, that's so bad.
why I disagree: she was drunk but she was the one who initiated the relation, and it wasn't caused by the alcohol intoxication. she wanted to be with him and hold back as long as she was sober.
he did nothing wrong, he was the one pushing her away for social reasons, and was also holding back because he loved her. that's absolutely understandable that he let his real feeling take control when she confessed her love.
she seemed to take a very active part in the sexual intercourse. it's not like she couldn't even move properly as she is the one taking off his clothes.
why I agree: you never know in this kind of situations and he could have just kissed her, even being nude and sleeping together without going all the way trough the sexual intercourse. the meaning would have been the same and they would have saved their first time for a more sober and conscious experience.
and now she doesn't remember her first time with him...
it's not something moral or ethical here, because they 2 were clearly consenting to the same thing. it's a relational pass: their first time is ruined forever.