Apart from the fact that I don't see the connection between sexual orientation and religion, this is (at least for a while) 2007, and a support site (I'm not talking about porn) for gay youth is as decent as a support site for farmers with tax problems, housewives with faulty appliances, or people with a medical condition. I thought bigotry stopped with the dawning of the age of Aquarius? ;-)
About 10% of the population wherever is not-so-straight, and it is a huge market, as Ellen spelled out in one of her blogposts on Dreamstime. Of course, a model can be used in a slanderous way, but that doesn't have anything to do with the orientation of the site.
If your model wants to act for RF stock, you should spell out that he/she has no control over the use, nor over the modifications of his/her photo. Modeling is just like acting in this respect: everybody knows an actor is not the character he plays.
What about muslims that don't want to appear on catholic websites or vice versa, vegetarians that don't want to appear on a Mc Donalds ad, macho men that don't want to be used in a womens mag?
Either you model for RF stock, or you don't. Nobody forces your model to model I suppose? If he/she wants control over the use, he/she should model for RM, or better, not model at all.
But if your model has second thoughts, me thinks it's only fair and kind to deactivate his shots on all sites and tear the contract apart. I had a similar case last year and I immediately deactivated the shots on DT. Since that incident, I clearly spell out to the models (who are also friends) the implications of the contract, included the "gay" issue. In my experience, models (especially teens) are very eager to model, but can't foresee all the legal consequences very well.