As far as I can tell, there are only a few arguments against gay marriage.
Most of them boil down to "It's against god's will", or "It will destroy the moral fabric of our culture".
Or similar phrases.
For the first, such an argument is neither provable nor disprovable, as it’s based on belief in an entity whose existence can, in turn, neither be proved nor disproved.
For the second, it is my understanding that this, also, can neither be conclusively proved nor disproved.
Although I believe there is more evidence against it than for it, only with full allowance of gay marriage, and ensuing tragic destruction of the “moral fabric”, would it be proven.
Personally, I think the fabric will just stretch a bit more…its more rubber bands than fabric…