That's not true. The Defense of Marriage Act enacted pursuant to Article IV of the Constitution precludes any other jurisdiction from having to recognize any marriage other than between one man and one woman. There is no danger to traditional marriage in any state that recognizes only traditional marriage. The issue in Massachusetts is one for the people of that state to resolve, and no federal constitutional amendment is required.
Any court that can find a constitutional right to partial birth infanticide will have no problem finding a way around the Defense of Marriage Act. It is ludicrous to think otherwise.
The constitutionality of this act is even questioned by some who believe in the original interpretation of the Constitution.