In a sane world, this would have been enough to disqualify him on the spot

[Labster]

Who in their right mind would go to a series of parties where that occurred, her saying it was not only well known but common?

Instead of trying to explain it, I'm just going to say that you need to watch Revolutionary Girl Utena (again).  High schools are almost self-contained worlds, and very few people are able to consider decisions outside of the context of their culture.  And even if they can, breaking out of a culture is highly disincentivized.