2. If a particular religious belief is dangerous to United States citizens, then it makes sense to use that religious belief as justification for preventing or controlling their entry into the United States.
3. People can make up whatever they want and call it a religion. In fact that is how many (all?) religions have been formed.
4. From 1, 2, and 3 it follows that it can in fact make sense to use a person's religious belief as justification for preventing or controlling their entry into the United States.
5. The Qu'ran can be legitimately interpreted to mean that Muslims should kill United States citizens: http://www.bloggersbase.com/politics-and-opinions/3-islam/
6. From 5, the Muslim religion is dangerous to United States citizens.
7. From 6 and 2 it follows that it makes sense for Muslim beliefs to be used as justification for preventing or controlling entry into the United States.
That being said, I still think the security guard was in the wrong. Clearly, our protagonist was not a problem, and the guard should have been able to discover that without stomping all over his rights. What's so hard about innocent until proven guilty? It ensures justice, even if the person turns out to be guilty.
This is controversial, because there are many Muslims who do not have ill intent toward United States citizens. I have good friends who are Muslim. Unfortunately, they have been raised with a religion that is potentially dangerous. Such is the problem with indoctrinating kids. I dropped the religion I was brought up with (Christianity) when I finally realized that it wasn't true and therefore shouldn't believe it. Perhaps Muslims need to do the same.
Most religions are innocuous enough that you can just let people believe what they want, and no harm done. But when leaving them to practice their religion might lead to them killing you, it's a little different.