While I don’t support same-sex marriage, this is the way it should be done, by states voting on it.
How about this:
While I don't support incest, this is the way it should be done, by states voting on it. Or:
While I don't support bestiality, this is the way it should be done, by states voting on it. Or:
While I don't support necrophilia, this is the way it should be done, by states voting on it.