There is no logic in any anti-gay argument. There is nothing that makes any sense, at all, other than what Magick already mentioned the church being allowed to not marry gays if they should choose so because as a religion they are free to choose not to under the constitution.
Other than that, any and all arguments are false and idiotic and if you agree with them you are a bigot and don't believe in freedom or America and should get the forget out of my country (see what I did there).
But honestly, I can prove the impractical logical falsity with a simple reductio ad absurdum:
Most conservatives believe that gays are immoral and shouldn't be allowed to marry, imposed by government.
Most conservatives believe that the government has no place in telling people what to do.
By this logic, the conservatives who believe gay marriage should be controlled by the state are not really conservatives, yet claim it's a necessary conservative value. Thus, absurdity, thus, handicapation.
Stop your bitching and let them get married you arrogant twats, I don't believe in your phony-bologna God or his asinine outdated book. Because of that fact alone, any politician who claims to not believe in gay marriage and that it's up to the state to decide has thus clearly stated they don't believe in the constitution or religious freedom and should get the forget out of my America. Same can be applied anywhere that has a constitution or other document that allows religious freedom in your country.
Let's stop these ignorant morons from getting away with raping our founding father's views for once and just loving legalize their damn marriages in all, I mean all, 50 goddamn states.