You're right. Banning politics is impossible. That's my point. I don't think anyone can logically argue against the stance that black lives matter nor against the stance that the LGBTQIA+ folk lives matter. However, by taking the stance that BLM masks are not allowed but other masks are allowed, Amazon is also taking the stance that black lives don't matter. Whether or not this is intentional, is irrelevant.
I'll give you an example of a workplace doing it mostly right. My old employer didn't do many things right, but for political stances, they did. "No graphics, logos, or lettering, unless Company's, on shirts, jackets, pants, etc. is allowed while inside the building, whether on shift or off" When covid hit, this extended to the masks with the "etc." part. When George Floyd was murdered, for example, some of the employees (myself, and HR, included) wanted to wear the "I can't breathe" masks. We weren't allowed. Some of us did anyway, and just prepared to take the write-up. The write-up never came, because corporate silently supported us and the stances we took. However, rules are rules, so we got a "talking to" and a tisk-tisk finger wave.
Banning potentially offensive political stances in the workplace is important to a degree, but you have to understand that some things are not political stances so much as they are supporting the lives and rights of other humans. After Amazon management staff had pools going on who of their floor employees would die next from covid during the start of it all, I highly doubt that the company understands (or cares about) the value of human life, so it's no surprise they're banning BLM masks from their employees. Whole foods, I know. But wf is Amazon.