If you took a poll on what was more sacred, marriage or the Constitution, marriage would win. That's why an Amendment of some sort will eventually be ratified.
The attempts to redefine marriage with which I'm familiar always look to expand it to include homosexuals. To which the predictable response is: "A bunch of activists are trying to shove this down my throat, and things are just fine as they stand."
There is a certain sacredness to Constitutional amendments. The document wasn't meant to be amended at whim, and people generally recognize that. Combine that with the fact that most folks won't see any genuine threat to their way of life, and what you'll do is alienate the moderates who are always - ALWAYS - turned off by socially conservative policy.
If you took a poll on what was more sacred, marriage or the Constitution, marriage would win. That's why an Amendment of some sort will eventually be ratified.