1) imposing your will on two people’s willful desire to be classified by the government based on their physical attributes
2) imposing your will on where somebody sits on a bus based on their physical attributes
They are the same thing. An arbitrary limitation based on color/sex/shoe size/penis/vagina/hairyness, and endorsed by the government.
Opposing gay marriage is the defacto support of social and economic stratification based on physical attributes. It is no different than saying that asians can’t drive on state freeways. Or that short people can’t be licensed by the state board of real-estate agents.
That position will be found to be unconstitutional at the federal level in due time.