But here from a brother's point of view his 15 year old sister first had her first sexual encounters(multiple times as she said) with a 40-50 year old man. I don't know how cool you would be in this case but most people would be very pissed. There's a reason there is an age of consent. It's very easy to manipulate growing teenagers. Many see it as their fault. If you as a brother are cool with it then that's you. Most people are not.
Also i think in other examples you've provided we know the characters. This teacher has just been ominously introduced and we don't know much.
Obviously, IRL I would also be angry.
If she hadn't lost it to Mr. Klaus but to her shitty (ex?) boyfriend, I would still be angry for losing it to anyone but me her beloved Brother. (Hmm, sounds kind of strange, don't you think?)
Anyway IRL I would prefer my close female family members staying virgins until their wedding (to a guy I approve of) and staying faithful to that guy until death. I also have to realistic and understand that life doesn't always work like that.
But this isn't RL, it's a game. And the MC is not me and Haley is not my sister. It's a story which the devs want to tell us.
My post was mainly directed against the NTR feeling that a lot apparently have, which is misplaced, I think.
And, in the games I mentioned, the MC is (or can be) also quite a douchebag and not that dissimilar to the (assumed to be) sexual predator that is Mr. Klaus.