In terms of public relations strategy, all Black Rifle had to do was nothing.

This. 100% this.

They could have very easily just stayed out of it. They were certainly not under any obligation to say anything. And, if pressed, they could have responded with a simple "We can't control the clothes people wear" or some such.

They put themselves in the middle of a situation they weren't a part of, and deserve every bit of criticism they get for it.