I suppose I should point out that I haven’t seen the documentary yet.
Is it Islam that allows men to have more than one wife but the man has to be able to support all his wives and treat them equally?
On the point about students being pro monogamy my guess would be that monogamy is such a culturally ingrained norm that even when you can understand that it’s a social construct on an intellectual level it still feels like the right and natural way for things to be.