I'm not sure that's true, but even if it is - isn't all of that covered by the first amendment?
The federal government would have good reasons to protect national security to question people that threaten our national security.
Edit: to be clear, I think Hasan is a fool, but detaining him still smells like a political purity test
I get that you don't think this is a problem. Just remember this when you are looking for someone that you can't find anymore.