The problem here is that loud people
tend to mistake their own loudness for popularity.
According to a new survey by the Public Religion Research Institute, only 41 percent of Americans oppose allowing same-sex couples to marry. But that same 41 percent has a highly skewed perception of where the rest of the country stands: nearly two-thirds of same-sex marriage opponents erroneously think most Americans agree with them.
So marriage equality opponents number only four in ten, but are pretty damn sure they are the majority because, hell, why wouldn't they be? The piece goes on to compare this behavior to, say, the surety of the Mitt Romney crew that they were going to win the election because all the polling was clearly a plot against them. It also shares quite a bit with the House Republican certainty that shutting down the government would be popular because it sounded like a good idea, etc.
While there's a certain mindset that presumes reality can be bent by sheer stubbornness (it tends to be the same crowd that believes climatology, biology, history and so many other things are plots against them, plots which can be undermined via the time-tested Tinkerbell strategy of clap louder), the more likely explanation here is that people who oppose marriage equality tend to travel in cultural circles in which everyone else opposes marriage equality, thus naturally presume everyone else in America thinks the same way their church group or bar buddies do. The only way they might be exposed to more tolerant opinions is if some television program some evening got all suspiciously tolerant and stuff, which is why "religious" conservatives have long stood sentinel to make sure Hollywood was properly censoring itself against such things. Didn't work, of course, but they still try.