Of course they do.
But, the military in general, and the USMC in particular, are very heavily oriented toward tradition. And, the tradition is that uniforms and issue apparel aren’t worn except for approved ceremonial purposes.
In particular, the campaign cover has a special and honored place in USMC tradition. To use it for political purposes, no matter how proper the politics might be behind the purpose, is... frowned upon, heavily.
I do not know the actual laws on the books regarding such things as it’s never come up in my own acts and actions, but I do vaguely recall that there are actual laws in place on such issues as well.
Who and what the heck are you trying to sale?
Some liberal Marine Sergeant Major selling his left wing junk?
Wrong. All you have to do is look at the intensity of the emotion.
A piece of gear doesn’t generate even a tenth of that kind of emotion. Racial politics do.
Why would you stretch so hard to defend the guy?