An amendment is far better for states rights than a federal statute. All of the states would have a say.
But it would be a one time say to get the amendment passed, and then you'd need 3/4ths of the states to ever get it repealed.
Imagine if an anti-gay marriage constitutional amendment had passed in the 1990s. You could have, hypothetically had 3/4ths of the states go along with it at that time. We would now have zero states with gay marriage in 2013, even if some of them wanted to pass it, because the constitution would forbid it. You'd need 3/4ths of the states once again to repeal the amendment, and that would be unlikely to happen any time soon.
Well yes, that would've been awful. So awful I'm surprised they didn't do it. All I'm saying is that the Rube's logic doesn't make sense. An amendment's process of being adopted fits nicely with the idea of state's rights overall. It also has the added benefits of bringing consistency to the law and requiring a nice majority to being adopted.