In certain instances, justice requires a secular government to eradicate a tradition. For example, the burning of wives upon a man's death was the tradition in India before the British jettisoned it. Beyond those rare instances, government rule should take great care not to disturb the customs of a people. I am surprised you do not believe in this principle. It helps to retain our liberty. Otherwise, governmental authority becomes too powerful when it becomes the sole arbiter of social structures.
Many traditions have been lost because they were contrary to human rights, fell out of favor, or just didn't fit anymore.
Which of these applies to the traditional definition of marriage as a union of one man and one woman?
I subscribe to the rubber band theory of social change. If you pull a rubber band out to it's extreme limit and then let go it lands way back toward it's initial position only stretched out a little bit. I think there are extremists puching the homosexual agenda that you see posted here often. They are on the outside of what most people think is acceptable. However the discussion around there activities will result in some change in the way society looks at homosexuals.
When I was a kid homosexuals weren't supposed to work in the state department or the CIA etc because if our enemies found out they would blackmail them. How could they blackmail them, well they were supposed to stay in the closet and not be know as homosexuals.
Things changed a lot since then. I think all of us are looking at the question what are homosexuals asking for and which of it should be denied. When NAMBLA says sex with kids, that's an easy one. Kids need to be protected from adult manipulation and abuse until they can take care of them selves. But there are those who would deny homosexuals teaching jobs and so on.
To sum it up, some changes will be acceptable in the US and some will not.
The second area is the use of governmental power to deny legal status to some and not to others. As a republitarian I support limited governmental power and when it is used then it must provide the same to all.