He doesn't believe in the First Amendment, that is why. Last I heard, unless one is under arrest, it is legal to move around the country or attend any events you wish.
The guy is a blowhard idiot who thinks he is president of afghanistan or something and his son is a horrible criminal. His only "crime" is being muslim.
None of the staffers recognized him or he would never have been seated there. If there is to be outrage about it, it would be against the secret service and the event staffers who didn't recognize him.
The guy is a looney tune publicity hound, just like Donald Trump.