Case in Point: Kathy Griffin. Holy cow that woman needs to get a grip on reality. She was so bent out of shape about the initial story that she wanted the kids names so she could publicly shame them and their parents. All because he wore a hat.
Maybe I'm going out on a limb here, but even if it were authentic Nazi uniforms worn in Auschwitz, he still has the RIGHT to wear it, and people still have the right to be highly offended by it. They don't, however, have the right to instigate physical violence on its behest.
Again, it's a hat. In an of itself, it's a hat with a very positive message. I feel that we all should do whatever we can to make America great again. Had Trump coined the phrase, "Keep America the same political cesspool it's always been", they would have been upset by that too. It all boils down not to what is said, but what is "implied". By saying Make America Great Again, it implies to some that America has somehow lost its greatness, to others it implies it was actually great at one time, and to others it implies that it was made great off the sweat of the (insert skin color of choice) working man's balls who had been forced to work slave labor in the hopes of one day achieving the "American Dream". The message is all in your head. For a simple 2 color trucker cap with only two lines of text, that's an incredible marketing tactic. It said so much to so many with so little. That's genius marketing.