I don't think opposition to gay marriage is very logical but I have seen respectful opponents of it shouted at and even called 'bigots'.
'Bigot' is very strong word.
The American Heritage Dictionary of the English Language (2000; bigot) defines a bigot as:
One who is strongly partial to one's own group, religion, race, or politics and is intolerant of those who differ.
Merriam-Webster online (Definition and More from the Free Merriam-Webster Dictionary) defines it as:
a person who strongly and unfairly dislikes other people, ideas, etc. : a bigoted person; especially : a person who hates or refuses to accept the members of a particular group (such as a racial or religious group)
There is a lazy stereotyping of opponents of same-sex marriage as behaving like members of the Westboro Baptist Church, when it is very clear that most are not. If one is tolerant of gay people except for the issue of same-sex marriage, and if one does not dislike them, one does not deserve this strong label.
I also note that some gay people are against same-sex marriage, and they are certainly not called bigots.
We can say that opponents of same-sex marriage are wrong, but if they are not motivated by hate or dislike and they tolerate gay people, it is inaccurate to call them 'bigots'.
Yet call them 'bigots' many people do; same-sex marriage is turning out to be the liberal shibboleth of this generation, and opponents are readily labelled 'homophobe' or even 'bigot'.
It is telling that some people are comparing opposing same-sex marriage to endorsing slavery, as if they were anywhere near similar.
Consider that again for a moment:
is the same as:
I think it is quite clear that equating the two is even more illogical than being against same-sex marriage.
Many of those who are fervently against 'homophobia' and 'bigots' are, I observe, not very nice people. Besides hating 'bigots', they can be nasty to other people who don't tick the boxes of 'people who possess characteristics protecting them from criticism'. I conclude that the urge to hate and to demonise the Other are endemic to the Human Condition - the groups we hate might change over time and depending on our pre-existing ideologies, but the hate itself doesn't.
I note that what is sauce for the 'homophobe' or 'bigot' is also sauce for the homophile - the demonising of 'homophobes' also has serious consequences, with at least one case of a shooting motivated by a hatred of 'homophobic' 'bigots' (Floyd Lee Corkins charged in Family Research Council shooting).
Indeed, I would venture that many supporters of same-sex marriage are themselves 'bigots', in their readiness to stereotype, hate and demonise the other side.