Jonah Goldberg rightly criticizes those Democrats now arguing against a Federal Marriage Amendment on the basis that the Constitution is a sacred document that should not be amended. First, no one, least of all the Founders, thought the Constitution so perfect that it shouldn't be changed. That's why they included the amendment process in the first place, and then proceeded to add ten amendments(commonly called the Bill of Rights) immediately after it was accepted. Second, the Constitution, as originally written, definitely gets some stuff wrong, particularly slavery and voting rights. Now I'll grant that what these Democrats really mean is not that it shouldn't be amended, but that it shouldn't be amended lightly. I agree, and I'm quite reluctant to amend the Constitution for something like defining marriage. However, these same Democrats are all for judicial activism which treats the Constitution as a "living document" that can be interpreted by unelected judges to the point of incoherence. This is hypocritical and unconstitutional. To the extent that the Constitution can be changed, or even re-interpreted, by anyone by any reason, that's what the amendment process is there for. It is no harder to remove an amendment than to add it: both are hard, but both are determined by legislators who face re-election every 2-6 years. A change in public opinion can, within the course of a decade, remove an amendment. Removing a judicial interpretation is much harder than making it. Making a US Supreme Court judicial interpretation takes an agreement of five justices, while removing a judicial interpretation takes an agreement of five justices. It's much easier to make than an amendment, and theoretically easier to remove. Justices, however, don't go up for re-election. They serve for life, or retirement. A complete turnover of the court takes decades, and even then there's no guarantee that the new justices will be in line with popular will. They're selected by one man, the President, then approved by the Senate (which, until recently, pretty much rubber stamped the President's selections unless there were real ethical problems). That's one degree removed from popular choice, and since one president rarely appoints more than a couple of justices, the court tends to be mixed.
I can respect those who are against judicial activism and an amendment. I can even respect those against judicial activism while for an amendment. I have a problem with those who'd cede our national will to a few unelected judges, then argue against the Constitutional and democratic way to express that national will.