Yes, a Constitutional amendment is needed here, but no, SCOTUS did not overstep their mandate. Their mandate is to judge the constitutionality of laws based upon the text of the Constitution. I've seen many great arguments on FR in the last couple of days saying why homosexuality is wrong. However, none of these great arguments are ones that SCOTUS can apply. As I said, their rulings must spring from the text of the Constitution. None of the arguments presented against legalizing gay sex are based on the Constitution. In order for SCOTUS to rule in any other way, the Constitutional text must say that gay sex is not protected or that no right to privacy exists.
Some people here have opined that all we need are "a few, good, conservative justices to vote the right way". Be careful what you wish for; you might get it. Alan Dershowitz gave his fellow gun-hating, liberal friends the same warning about the 2nd Amendment...
"Foolish liberals... are trying to read the Second Amendment out of the Constitution by claiming it's not an individual right or that it's too much of a safety hazard. They don't see the danger in the big picture. They're courting disaster by encouraging others to use the same means to eliminate portions of the Constitution they don't like."Conservatives ought to show equal concern at conservative justices playing fast and loose with the Constitution. What we allow today, liberals will allow in the future. And as surely as night follows day, there will come again a Court with a liberal majority. We should be careful what rules we establish for their behavior."The Conceptual Foundations of Anglo-American Jurisprudence in Religion and Reason," 62 TENN. L. REV. 759, 789 (1995).