I'd never thought someone would be that paranoid! As a Christian, I'd be more worried about promiscuous heterosexual activities, which are far more likely to occur between teenagers.
But seriously, I know Christian parents that would argue your last point, saying that separating the genders is overkill, and that it would be better for them to deal with their urges in a co-ed setting. The point being, not all criticisms of gender segregation would come exclusively from the Left, though they are the most likely suspects.