There is no way on earth that anyone is going to make a court case over this. It's hardly discriminatory and winning would involve removing everyone else's right to religious belief and government interjection into biblical interpretation.
Get real, forget it.
They believe that god has promised a paradise and won't let certain people in. Boo hoo. Not being welcomed into an imaginary land is as discriminatory as not being included as a character in Alice in Wonderland. No one is going there anyway, it's make believe.
Lots of other people aren't invited too, not just gay people. There are more than gay people lumped together in the bible verse they base it on.
As for the choice vs non-choice - they would argue that it's not about being gay, it's about being immoral and everyone has (should have) a choice of whether they are sexually active so based on the bible view, it's no different to non-gay people having sex outside of marriage. Of course the fact remains that they don't allow gay people to marry - based on scriptures like that. So round and round the circular reasoning goes.
But damn, if anyone is really offended then they should take legal action to ensure that they are invited to the imaginary land they don't believe in.