I already mentioned that marriage, kids, and a mortgage are very strong indicators of conservatism. Here’s a straightforward causal explanation: when you’re invested in something, you don’t want it to be taken from you, and you’re skeptical of starry-eyed meddlers doing anything that might threaten it. Probably the best thing done for the cause against gun control was teaching others how to use and maintain a firearm: once people own one, it sharpens the mind to cut through any argument for taking it away.
But a gun is a small investment compared to a committed and intimate relationship, custody of children, and homeownership. A dollar taxed is one that you can’t spend on your family when they want something, a dollar borrowed is one that your kids will pay back, and that meddler on TV is rolling the dice with a major part of your life.
In the case of immigration, Hispanics are already primed to be conservative because they’re already invested. With gay marriage, you have a group trying awfully hard to get more invested.
The conservative argument for embracing gay marriage is that marriage seems to be a fine institution that benefits even people who can’t have children together, and that it may strengthen the institution and the country to expand the institution so that a nontrivial minority of the population is on the inside trying to protect it rather than on the outside where their exclusion leads to thorny political issues of respect and tribalism.
Another conservative argument is that if gay marriage is politically inevitable, conservatives should proactively move through legislation to ensure that it goes smoothly without infringing on other freedoms (like those of association and contract), rather than allow this to play out entirely in the courts or in a referendum. If conservatives keep trying to board the windows, more stuff is going to end up broken than if they just opened the door.
As with immigration and Hispanics, marriage may not be gays’ top priority, but it matters, and the way Republicans approach and discuss the issue can signal that “you’re not one of us,” which is poison for coalition-building.
The flip side of that coin doesn’t have to be pandering; given the consciousness of gay communities about targeted violence and bullying, it’d be awesome if conservatives taught more gays how to use and maintain firearms.