The 'calming' incense was indeed that, but I don't know about you, that IS still considered as drugging him, you know XD? Same one was also being used on Asuna, so they couldn't think straight, but they STILL stimulated their desire: If it wasn't obvious before, in the scene of Liz 'practicing' with Inoda you can see in the rec. room we get the full clarification that they were both using a special massage that 'stimulates desire' (Through some dumb NTR logic that shouldn't make sense even in VR but FOG is filled with XP). They WERE specifically getting both of them horny.
Mind you, you're right that it IS still Kirito's fault as you still have the option to refuse, so yeah, but the only reason said option is brought up at all is because Kirito is being messed with by more sources than just teenage horniness XD
Kirito IS being corrupted, without a doubt, but I always thought that was just what Fujino was going for to justify later the "becomes a willing cuck" ending than anything else, tbh.
Also, LMAO, now I really want something like that to happen, I almost feel tempted to suggest it word by word to Fujino in the next progress report
Because hey! Technically, "he got drunk and fucked his sister cousin in the shower", then becomes his sex slave out of 'guilt' by being told he has to 'take responsibility', does not contradict the "Kirito never finds out" Ending! He still technically doesn't know Asuna is being NTR-ed, he just landed himself into a much worse problem that he can never let Asuna find out, hilariously enough XP