One of the problems with homework questions is that they often get an answer before the question can be closed. So the vile perpetrator gets the answer they want, and the subsequent downvotes don't hurt them because their rep is probably already just 1 and they may not be planning to come back anyway.
I'm sure anyone posting answers to homework questions is just trying to be helpful, and I doubt they have the destruction of the site in mind, but I wonder if some sanction would be appropriate. The obvious one would be that upvotes for answers to questions closed as Off-topic would be excluded from the rep (I wouldn't exclude the upvotes from the rep for other close reasons because some questions closed as duplicates have good answers). Could we ask SE if they can do this?