Whatever the Bible says on the issue is irrelevant as it only pertains to people who believe anyway!

For good or ill, that's not so, Allan. Remember we are talking about the US here, where there is a strong religious element and that that element can be in positions of power enabling them to affect non-believers as well as believers. So what the Bible says can be of life-altering importance to non-believers. Now, I personally agree that "it certainly should not be allowed as an excuse for discrimination" but that's a lot more subtle than it sounds, especially if you happen to believe the Bible is unerringly true and that you understand it perfectly, as some of these people do. If that is your mindset then preventing gay marriage is no more discriminatory than preventing murder. I don't agree, of course, but that's how the thinking goes.