Also, there are already protected classes that are partly or wholly matters of choice. Religion, pregnancy, familial status, veteran status.
On a related note, I don't see that the is it a choice? question is even meaningful in the first place. Preferences aren't generally something we get to choose. I could probably learn to like some unfamiliar genre of music simply by listening to a lot of it, but you could offer me a heap of money to like the PHP programming language and I'd still be unable to do so. My opinion of it isn't something I can so easily will to change.
On a related note, I don't see that the is it a choice? question is even meaningful in the first place. Preferences aren't generally something we get to choose. I could probably learn to like some unfamiliar genre of music simply by listening to a lot of it, but you could offer me a heap of money to like the PHP programming language and I'd still be unable to do so. My opinion of it isn't something I can so easily will to change.