@valconius: I understood you.
Virtue is not a trait that's inherent to man, civilization is not mankind's natural state either. At man's core, he's bestial, thinking of himself before anyone/anything else--if he thinks of such at all. It takes effort to elevate oneself above such a base state, to embrace being genuinely good; children, in their immaturity, are that way because they lack the knowledge and the fortitude to make that climb. Adults who stay immature (and very many stronk, independent Modern Women can be counted among them) are that way only because they lack the latter. Both concern themselves with #1 (whether immediately or ultimately) first, even to the oblivion of everyone and everything else.
With that said, and in keeping with what I said in the second sentence, it's easier to feign virtue than to actually possess it; to ignore your ego and your desires to make virtue the goal. Those who do the things you described only seek to a) build their own value in the eyes of others, so that their ego is fed or b) build their own self-perceived value, also so that their ego is fed--but, of course, in a different way. The people who engage in this sort of behavior would never accept that the hand must be hardened in order for justice to be served, or that it must become a fist to strike down injustice--but, as a means for those with insight to discover the true nature of the faux-virtuous just as lies are always discovered at some point, they are frequently happy to strike down those who transgress against their emotions. After all, ego, emotion, and the service thereof are all they truly have, not virtue.
Hoshino, here, is no victim to anyone but her own vices. She wants celebrity at any cost; she's the type that would have gone to Harvey Weinstein for success. In a manner of speaking, that rooftop was her casting couch, Doi was the licentious director, and the choice was made long before she got up there; she just didn't realize how immoral her choice was until <i>other</i> people were around to see it. The actual victim is Doi, however. Acting as the UW's proxy, Kamiya subjected him--an already broken man who could have been healed through Yuzu-sensei--to much abuse of various sorts; sending Yuzu-sensei (after promising that Yuzu could stay with him if he would sex the other girls) away was the straw that broke the camel's back, at least for his morality. Yuzu was his way toward proper healing and development; with that way sealed off, all that remained was Kamiya and her path toward dissolution.
The only reason someone would defend Hoshino (as they do in seemingly all anime/manga that show a woman in this sort of situation: some examples are Tate no Yuusha no Nariagari, Kaifuku Jutsushi no Yarinaoshi) is because they're not only conditioned by traditions to see women as entities they must always protect, but they've been conditioned by modern progressive thought to believe that a woman can never deserve any ill fate that befalls her, and that--should it be a man who visits said fate upon her--it is always that man's fault.