It is a motte and bailey argument, most people agree with gays having access to legal marriage, the contentious part is religious marriage. Should we force preachers who don't believe that homosexuality is kosher to wed gay couples? A lot of people don't think so, and then they say they are against gay marriage even though they would be fine with legalizing them getting a legal marriage.

For example, do you think that we should force Muslim Imams to wed gay couples? I believe that it would be a fairly controversial topic even in left-wing circles.