I see your point, but there's also value judgements with other categories. How is an "adult" or "pornography" item defined?

Personally, I don't have an issue with a business choosing to ban or allow items as it's their platform and their business choice. If they choose to not sell any lithium batteries due to their flammable nature, then that would also be acceptable and not in my mind dystopian. There's arguably some risk in being involved with sending potentially offensive media through the mail.