I think it’s mostly a combination of people being against incest on principle, and people just not liking Kirino. Both of which I think are silly, but what can you do.
I quite enjoyed that part of the ending, actually.
I still don’t see a problem with mutually agreed-upon brother-sister incest. In fact, I’d have been dissapointed if they’d bailed out and taken the safe route.
I would like to think that Im seen as smart and can critically think (well, I hate when anime makes us critically think, it should be simple and streamlined), though I hope I dont have pessimistic or er cynical comments.