People meet each other before their thoughts on gay rights, or really any thoughts are known. I would say physical location would be more of an indicator of whether or not you'll meet someone gay. If you go to the Castro for example, it's much more likely you'll meet someone gay than if you are ... well, I dunno, somewhere there aren't a lot of gay people.
Why couldn't one conclude that the #1 predictor for whether or not someone will meet someone who is gay is how they side in issues of gay rights?