If there were no state benefits for those married, of course. But there are. Both opposing gay marriage AND not opposing that benefit system is patently discriminatory - how could it be anything else? It is saying 'there is no way you are going to get the same benefits as other people, because of whom you happen to love'.
I was under the impression that a sizeable amount of people are against gay marriage for purely symbolic reasons and that they would be fine with civil unions, which would grant all the same legal benefits of marriage. Under this scenario opposition to gay marriage seems more like a political/religious belief rather than a civil rights issue.
It seems like a semantic belief in that case, which doesn't seem to be worth spending $1,000 on, let alone the rest. Unfortunately, I don't share your optimism: I suspect that many of those objecting have a pathological dislike of gay people.