You should also read the Constitution. It has been used to restrict an individual’s right to their income and to drink alcoholic beverages.
Your claim that believing this should be left to the states indicates “softness” on the issue is fallacious. It’s even more so when you broad brush them as “social liberals.” I tend to fall on the state rights side of this and I volunteered for the Prop. 8 campaign here in California and did quite a lot to help get it passed. So clearly I’m not soft on the issue nor a social liberal. I just don’t like the Constitution being amended needlessly and think that should be preserved for only the most needed of circumstances. You seem to be adopting the liberals’ argument of the constitution being “a living document.”
As to your other point, many would argue the use of the constitution to institute an income tax or to ban alcohol was an abuse of the document. Just because it’s been abused before doesn’t make a good argument for doing it again. And as I pointed out in my follow up post, I did recall the institution of prohibition. But notice it was repealed. And one could argue the imposition of an income tax at least applied to all and didn’t just single out one group for penalty. I think my argument remains in tact—that the constitution should not be used to target individual groups in denying them privileges. Let the states work it out. As I mentioned, most are making the proper choice to say thumbs down on gay marriage.