Because society places a value on masculinity gay men aspire to it. If you go to a gay club and the doorman says 'You do realise this is a gay club don't you lads?' you get all excited because you think 'Wow he thought I was straight!'
I left school at 16 but I wish I'd gone to university - I think I would have studied English literature. I had a knack for that. But I don't think you have the kind of wisdom at 16 to make that decision.
