It is a choice but it doesn't seem so because it's a manifestation of a cultural mental imbalance in the individual so they will never see it as being the flawed perception it is, they will always try to justify it as biological.
Such is why you see such heated posts by gays. Subconsciously they know it's a choice but they could never admit that or they'd essentially be confessing that it's actually simply the equivalent to a child playing pirate. It is possible to choose not to as evidenced by 'bisexual' people. At least that group admits it's a choice openly so.