The fact that many people can't recognize a legitimately insane person when it's right in everyone's faces is pretty indicative of why our society fails to help people with mental illness. If he was a sane person who simply had controversial ideas and opinions he would at least show signs of nervousness and hesitation especially when speaking to the media. But he shows none. This is not normal, of course, and is a sign that something is not working right in his brain. And it's not just that his opinions are controversial, they're downright antisocial.
This guy sent a letter to the secret service threatening to kill the president. What sane person would openly break the law and send the evidence to people who could get him arrested? Only a crazy person, that's who.
But for some reason most people are taking him seriously. Rather than having compassion for someone who is in obvious need of help, people are threatening to kill him.