Veteran denied entry to Six Flags for wearing ‘Keep Calm And Return Fire’ shirt

I know this experience personally, mine was at Sea World two years ago, wearing a USAF shirt which has a F-15 jet dropping bombs, but there is no ground in the image so one can’t tell a target. But, it was offensive and I was denied entry. WTF people? There can be offensive language, religion, and your favorite product, but nothing military. Isn’t that just beautiful?