The TSA could've made him change the shirt before allowing him into the Sterile Area. Jokes about bombs in an airport are taken VERY seriously. They obviously screened him and determined that he was merely an azzhat, who was exercising his rights while judgement impaired. That's the part everyone forgets. Just because you have a right, does not MAKE you right. You can be fully within your rights and be completely wrong. Your 1st Amendment rights allow you to burn the US flag as a form of protest, but you're wrong if you do it. The Delta pilot recognized that this guy was wrong, exercised his judgement as Pilot In Command that it would cause civil unrest on board the aircraft and denied him passage. As PIC, that's within his authority.
With rights come responsibilities. Some people care nothing about the responsibilities, only the rights.
I agree, but make that a lot of people.
Before anyone says anything, I stopped flying commercial because of all the stupidity so I am not a fan of the TSA or the airlines.