https://www.amazon.com/nevoli-Murder-Adjustable-Baseball-Fashion/dp/B096GXB26X/ref=sr_1_2?dchild=1&keywords=blue+lives+murder&qid=1623327482&sr=8-2
"We do not endorse the content of any particular book, video, or product," an Amazon spokeswoman said."
But you do ban other things because they're potentially hurtful (See "When Harry Became Sally"), and therefore, Amazon permitting the ball cap is an implicit endorsement.
