Yes it's a public airport. No one is saying that this guy went parading down the aisle of Kerry headquarters. Now, let's examine the central questions here:
I'm all for civics lessons, but c'mon, isn't 3-years a little young for the civics lesson that there are jerks in the world who will scare you and tear up the pretty sign you're holding?
There is no reason that a union thug should be allowed to do this. If you tried to do this to the union they would cry and beat you with a baseball bat. I have lost all respect for any union if they do not fire the goon and say this is bad.