At least for me, it's not about seeing them do the deed. I'm not all that bothered by it. It's moreso that we expect teenagers, when presented with the opportunity for it, will more likely than not agree to do it. In this instance, Sora does not seem to really entertain the idea much, beyond a brief lapse of judgement. He then calmly lays out the case that he feels they are too young to be having that sort of intimacy.
I'm fine with teenagers having reasons to put off physical intimacy, but it's getting kinda tired where we frequently have female characters eager to do the deed, and the male protagonist being the paragon of purity going "hol' up, let's wait till older", which doesn't feel like a realistic portrayal of teenage relationships and seems more like something inserted by the morals police to make sure we all get that, hey, people under 18 should not be having intimacy, that's strictly reserved for adults, this relationship is nothing but wholesome.
It stinks because it doesn't read credible, not because I wanna read about kids having hanky-panky.