Don't get me wrong I was agreeing with you. I just wanted to draw a distinction between a person's ability to have sex with a person of the same or (opposite) gender and their core sexuality.

I would define a bisexual as someone who can only find fullfilment in having relationships with both sexes.

While some gay men might have the capacity to have sex with females, if they can only find emotional and sexual fulfillment with other males I'd say they were not choosing to be gay they were choosing not to exersise the option of having heterosexual sex.

Equally a straight man who might have the capacity to engage in gay sex but doesn't isn't choosing to be straight either he's just choosing not to exersize a redundant capacity.