Was it right for Six Flags to tell a veteran to leave because of his shirt?

A US Marine Veteran was denied admission from Six Flags Great Adventure because of the content on his shirt.

The veteran, Mario Alejandro, was wearing a shirt that said 'Keep Calm and Return Fire,' and it had a picture of a gun before the saying. Security offered alternatives to Alejandro so that he would be allowed in the park, but he denied and was escorted out. Alejandro was sure to let others know that he believed this was a reflection of how the park treats veterans.

Should Alejandro have been escorted out? Many feel that it was his right to wear the shirt, and that it was not offensive to others. Others are saying that the veteran was wrong to react how he did, and he shouldn't feel above Six Flag's policies because he served for our country.

What do you think?