Terrorism requires tools, but it also requires a motivation powerful enough to lead people to kill — and to die. Guns are sometimes the tools. And radical religious figures and radical friends sometimes help provide the motivation.
Say that the president had said:
Congress should act to make sure no one on a no-fly list is able to [hold a position at a mosque, or have gatherings of people at his home]. What could possibly be the argument for allowing a terrorist suspect to [do something that could lead others to become terrorists]? This is a matter of national security.
I would sharply condemn such a proposal, and I hope others would, too. If someone is convicted of terrorism, they can be imprisoned. If they’re suspected, they can be monitored. But you can’t take away people’s First Amendment rights based on suspicion, even if the suspicion is that the people will use those rights to help cause terrorist acts.
What the president actually said was:
Congress should act to make sure no one on a no-fly list is able to buy a gun. What could possibly be the argument for allowing a terrorist suspect to buy a semiautomatic weapon? This is a matter of national security.
And my reaction to that is the same, on Second Amendment grounds, as my reaction would be to the hypothetical no-preach/no-organize-meetings proposal.
For more, see this post.