He was still nuts. We know that's the kind of people you want to be armed.
Nuts is a pretty broad definition, what's going to be considered "nuts" and how is the government going to fairly apply "nuts" without infringing on people's constitutional rights? What about "nuts" and harmless? Should they have their rights stripped? It's very hard to make the distinction of whose dangerous and whose not, especially when it comes to people who are "nuts". There's a lot of them out there that claim a lot of crazy things like this guy did, and a large large majority are harmless, and just need help.
This guy didn't even need to be on a no fly list (which is a whole other BS issue), to commit this crime. Even if he was, he still would have been able to commit it since he snuck into baggage claim.
And again gun control would not have worked to prevent this crime, or many of the mass shootings we have seen. San Bernadino shooter was not clinically insane, just fanatical. He worked for years among the non fanatical without any problems.
If you want to do something that will actually work, we have to stop giving these killers notoriety, and encouraging the very few crazies out there to do something to make a splash and be all over the news.