Free Speech Limits

I want to ask you about free speech, or rather, the limits of it in a democracy...say a democracy like Britain's or Australia's. Wouldn't you suspect that speech would only be limited when it caused injury? Maybe or maybe not, according to Aussies. Apparently, Australians like George Bush more than we do here in America., and perhaps some of them at the Melbourne airport like Bush more than free speech itself. Given that Bush's popularity rating in the U.S. is only about 35%, that's saying something. I write this because of what happened in Melbourne, Australia recently.
An airline passenger, Allen Jasson, 55, was barred from a flight for wearing a T-shirt labeling President Bush a terrorist. He could be right! And Allen is now threatening legal action against Australia's Airline Qantas. for giving him the boot from the flight. Allen is an Australian IT expert who lives in Britain. He was stopped by Australian security from boarding a London-bound Qantas flight at Melbourne Airport last Friday while wearing what the airline said was an offensive T-shirt. Airline staff said the T-shirt of Bush with the tagline "World's number 1 terrorist" could have upset other passengers and demanded it be changed for another. Haha It also could have made the passengers break out in agreeing applause.
But Jasson, who had earlier traveled on a Qantas domestic flight wearing the Bush T-shirt, said his right to freedom of speech had been infringed by Qantas. "I am not prepared to go without the T-shirt. I might forfeit the fare, but I have made up my mind that I would rather stand up for the principle of free speech," Allen told Australian media. Of course, he also said that he would seek legal advice.
Qantas issued a statement saying comments made verbally or on a T-shirt which had the potential to offend other travelers or threaten the security of aircraft "will not be tolerated." The airline implies that violence would erupt on the plane between a Bush admirer and Allen, simply because Allen wore the shirt. Isn't that an assumption, and isn't the airline placing their assumption ahead of free speech? Or was it necessary to ban the shirt to protect passengers from violence that may have erupted on the plane because of what the shirt said about Bush? Does denying free speech because giving an opinion about a public figure it may "offend" someone make sense to you. I think Bush is an idiot and a menace to world peace. Though I doubt he's a terrorist, I think I would be a "terrorist" (I am using that term loosely here, as that fellow Allen and the censors at the Melbourne airport have done) to deny others a chance to express their opinion.
Frankly, I do not think any U.S. Airport could make Allen take off the shirt, that any U.S. courts would say that he could not express his dislike and opinion of Bush. What do you think would happen if Allen worse that shirt while boarding a plane at your local airport?