I do not think that the arguments against gay marriage are all grounded in bigotry, and I find some of the arguments persuasive.
Here's the thing. The main arguments against same-sex marriage are (1) the argument that it will cause some harm to society and (2) that the argument from nature against homosexuality. But, nobody has identified an actual harm that same-sex marriage is going to cause to traditional marriage or that gay adoption will harm children. So, it's not so much an argument from harm as it is an appeal to fear based on some perceived harm. And, the argument from nature has some seriously problematic assumptions and implies some pretty counter-intuitive moral conclusions.
I have a difficult time seeing how these arguments are "persuasive" after you look into them, even just a little. But, I'm pretty sure these arguments are not rationally compelling. The fact that the people I happen to run into give these arguments arbitrarily against homosexuals - rather than follow the logic of their own arguments in a principled and consistent way - that makes me wonder if their opposition to gay marriage is rooted in bigotry. Is it so crazy to think that it's probably the case that a segment of the population engages in motivated moral reasoning in regard to homosexuality?