wait, what?

I don't see why there is such a deep divide in the Democratic/Republican party philosophies and some of their actual stances.

My understanding of each, in a nutshell:

Republican Philosophy: Republicans champion the Bill of Rights and favor minimal government intervention so that the individual can retain as many rights as possible. One source says, The purpose of government is to ensure that the rights of the individual are protected, and at the same time the government must restrict its activities to providing only the services that individuals cannot provide alone, such a national defense.
Republican Stance: Against gay marriage

Democratic Philosophy: Sacrifice individual rights for the "common interest"
Democratic Stance: Pro Gay Marriage

Obviously this is a highly generalized, crude analysis, but I can't help but think that for both parties the stance is inconsistent with the philosophy.

Now, wouldn't legalizing gay marriage be a victory for expanding the Bill of Rights? and strengthening the rights of the individual? And, oppositely, wouldn't keeping marriage between one man and one woman benefit the "common interest"- satisfying the needs of the heterosexual majority??

I just don't see the logic here...