You should be asking: "In what way are you for or against gay marriage?", as you can have both a personal opinion and an opinion with regard to politics or to the public. For instance, I answered the poll question as "against" due to me personally being against it, but legally it is an entirely different matter.
My personal feelings are that, within my family, and with regards to raising my children, I will not tolerate homosexual marriage, and it will not be discussed or given any credibility in my home. Homosexual behavior ceases procreation, and therefore it serves no meaningful purpose, and is merely a social act with no significance.
Since government is involved, and that won't be changing anytime soon, my political opinion is that homosexuals cannot be prohibited from a legal marriage, as a government/ paper marriage is meaningless in the eyes of everything except the law, so therefore what does it matter to heterosexuals like myself if homosexuals commit to a legal marriage or not? I don't like it, I never will, but there isn't any reasonable legal basis for prohibiting it.
I should add, though, as I have in other threads about "gay marriage", that it is quite a double-standard for the people who advocate for these so-called "gay rights" when most of them would be horrified at the thought of legalizing plural marriage. I don't see any difference between the two. If marriage is something that is perfectly suitable to non-heterosexual people, why is it so bad for non-monogamous people to be legally wed? You support homosexual rights but not non-monogamous rights?