Isn't it a privilege to fly? Not a right. It's not like an airplane is some public government arena. It's the property of the airlines, just so happens that you have to be cleared by the government to fly. Don't they have the right to refuse service to a customer, especially if that customer is making employees and other customers uneasy. I'm sure if you went into a McDonald's and were wearing some suspicious clothing or start spouting off ridiculous speeches, they'd ask you kindly to leave and tell you that you were not a welcome customer any longer. In fact, I've seen it happen.

There are places for expression and "Free Speech"... maybe sitting next to the 13 year old or grandmother (or any other paying customer) who's flying for the first time in his/her life wearing some silly t-shirt about bombs and anti-government banter isn't the right place for it.