Sam took advantage of Dean being drugged/drunk and Dean didn't specifically consent to sex on that night, the boys had discussed it beforehand and Dean's consent is implied because he has a safeword and chooses not to use it.

A lot of what you say in this post is very interesting, but I find your explanation that that story is fully consensual somewhat unsettling. Even if Sam didn't purposefully drug Dean, he "took advantage" of him being non-consensually drugged by equally non-consensually stripping him, trussing him up, and gagging him while he was unconscious from drugs he had not agreed to take.

Yes, AFTER all these non-consensual things had been done to Dean, he did not use his safeword when he was no longer unconscious (given that he's still drugged enough at that point that he can't remember anything that happened, I'm not sure how valid that consent is, but that's a point for another day), but unless they had specifically discussed, and Dean had specifically agreed to, Sam doing all those things to Dean when he was drugged and unable to say no (and when he had not consented to being drugged), Sam had no consent, implied or otherwise, and the fact that Dean eventually enjoyed despite the advantage that had been taken of him doesn't change that fact.