As much as I agree with with Longtooth said about the constitution, here's how I think the reality is (and why I support a law)
When someone in the government has an idea to do something, they might check laws to see if they can do it, and how they should. If there isn't a law saying they can or they can't, they'll do it anyway, in a rotten fashion. Look at HOW the arms confications happened. (ignoring the fact that they happened at ALL.)
It seems that the officials in New Orleans just grabbed guns and threw them in a room. They didn't do anything to keep any records of who they took from who, etc.
Texas might be gun friendly now. What if that changes? What if, in 5 years, the head of DPS is a gun grabber? Or, worse, what if the Governor is one?
If we pass a law to protect our rights, now, we're far better off.