Well, I think the constitutional ammendment part of it was to stop all the judges who decided the best way to institute social change was to assume the power of a couple other branches of government since they were taking far to long to get things done. Regular laws weren't standing up against that, so the only appropriate response if you are concerned about protecting the current definition of marriage, is to make an official ammendment that rules out any of the loopholes the judges were using to legislate with.

Note I'm deftly avoiding the, "why is gay marriage objectionable" issue as you are already involved in that discussion elsewhere.

Dan