“So, having established the value of gay marriage, why are people so opposed to it?”
Because if you don’t say you are in favor of it, you are harrassed, your churches are attacked and vandalized, you get assaulted, you get called a bigot and violator of civil rights, and you are forced from your job (the theater director in Sacramento being the first example).
Isn’t it interesting to see how voting is not a protected right, after all, the theater director was forced out for backing ads for a proposition that was on the ballot. We can assume he also voted for that measure.
But political beliefs are not protected from discrimination as religious beliefs, sexual beliefs, sex, and skin color are.