I just came across an interesting post by an author in the U.K. He pointed out that gay marriage could be viewed either as an issue of equality or as an issue of freedom. Seen in one way, the argument for it was that homosexual couples were entitled to the same rights as heterosexual couples. Seen in the other, the argument is that people are entitled to marry whom they please.
It can be viewed either way but, he argued, in practice it was framed as an issue of equality. His explanation was simple. The right, which was against gay marriage, was much more comfortable criticizing arguments from equality than arguments from liberty. The left, which was for gay marriage, was much more comfortable making arguments for equality than making arguments for liberty. So both sides agreed that what the controversy was really about was equality.
I suspect his point is more accurate for the U.K. than for the U.S., that the liberty argument plays at least some role here. But his distinction may be relevant to one feature of the argument as I observe it. In the U.S., one argument against gay marriage is that, if it is accepted, the next step is polygamy. Supporters mostly deny that there is any connection, rather than arguing (as I think they should) that polygamy too should be legal.
If the argument is about equality, one can plausibly deny any link to polygamy on the theory that as long as nobody is entitled to be married to more than one partner at a time, everyone is equal—more plausibly, I think, than one can make the corresponding argument against gay marriage, that everyone is equally entitled to marry a member of the opposite sex. If the argument is about liberty, on the other hand, it would seem to apply just as strongly to the case of polygamy. So in this case, the right seems to prefer to view the case for gay rights as a (mistaken) argument about liberty, and only the left as an argument about equality.
I am curious as to how that part of the argument plays out in the U.K. Readers with expert information are invited to comment. And I may put the question to the author of the post.