No; it's not good if, in defending marriage, the government steps outside of its Constitutional limits. This is almost the exact same thing that happened with the War on Drugs
and the 4th Amendment -- because "drugs are bad" & "drug dealers are bad" we allowed the police to violate the 4th so much that the 4th amendment is now virtually gone. (As evidenced in the NSA revelations, and the TSA's general operations.)
Indeed, CS Lewis commented on this mentality:
Of all tyrannies, a tyranny sincerely exercised for the good of its victims may be the most oppressive. It would be better to live under robber barons than under omnipotent moral busybodies. The robber baron's cruelty may sometimes sleep, his cupidity may at some point be satiated; but those who torment us for our own good will torment us without end for they do so with the approval of their own conscience.
— C. S. Lewis
Remember what was said: A government powerful enough to give you anything you want can take away everything you have.
Here we have Tonto, Tarzan and Frankenstein to weigh in.
Tonto: "Fire good."
Tarzan?
Tarzan: "I think that fire good, too."
OK, now turning to Frankenstein, what do YOU think of fire?
Frankenstein: "Fire Bad! Fire Bad!"
Frankenstein goes crazy and breaks through the back wall of set.