Typically, older teachers who sleep with a lot of students do abuse their position and authority in order to be able to do it. Whether by giving favorable/unfavorable grades, by visibly preferring some students or by more direct threats.
> moralist, religious-derived, US-centric concern
Then again, if teacher touches you inappropriately in US or is trying to manipulate you into that, you can actually complain. It is not easy and you may not be believed, but you are is still in better compared to less moralist places.
It is not exactly US-centric concern to think that any of above happen. The same happen everywhere. It is that complaining about it in US is not a taboo.