>If we enforce some morals and not others in our app stores, who exactly do we choose as the arbiters of morality?
Apple and Google are, and their moral guideline is money. They are in the business of making money. If the content seems close enough to illegal and small enough revenue to not be worth investigating it, or if the content is legal but costs more to host than it brings in due to backlash, it will be censored. I would even guess that content that is illegal but brings in enough money won't be banned (unless a court order comes in that isn't worth the cost to fight).
One can just look at Reddit's history of banning content and see that it bans things not based on morals or laws but on when it stopped being a revenue generation. The allowed their most popular sub-reddit for years until moral outrage grew due to a news investigation, and then banned it under the guise of being illegal and protecting minors (despite the content not being illegal, as the federal government wouldn't have allowed to continue operating had it been).
Don't Apple and Google already block plenty of legal content they don't want to deal with? Consumers should force them to explain why they are willing to deal with this specific content.