This story brings to light several issues...
First and foremost, how much does ones right to free speech supersede the government's right to protect its citizenry. How much right does the USA government have in this case to deny entry in cases such as these?
On the other hand, the tourists are coming into the country as guests, what role and responsibility do they have to show proper respect for the nation to which they are about to enter? I am sure the gentlemen (and I use that term loosely in this case) meant no harm, what if they had and the USA government chose to ignore it due to free speech concerns? Would the citizenry be okay with that trade off?
This is an area with a lot of shades of grey and is and issue that is going to become more prevalent as social media puts more of our thoughts and ideas out into a global environment. Perhaps, if nothing else, we should think twice about how our social media positing could be interpreted by others.