The thing is that from what I've read, with these content bans Visa and Mastercard are being lazy and bean counting rather than morally motivated. Remember that they have to comply with commerce laws across basically all worldwide jurisdictions at the same time. To give you the example of loli hentai: Possession is legal in most Western jurisdictions, but illegal in France, if largely unenforced. That still means that Visa and Mastercard's Know Your Customer teams need to set up a local branch that in theory should be scouring the Japanese porn sites to make a list of that content, flag it, and set up a reporting system to the National Police every time a transaction is made on a French card. Otherwise it will be their arse on the bench for facilitation the day some nonce gets dragged to court and they find both real and drawn CP in his hard drive.
They do that for items with a high volume of transactions: India and Nigeria have blanket bans on all porn that they are apparently somewhat diligent on enforcing, but the amount of money the more vanilla porn sites move around makes it worth it to them for the transaction fees in the rest of the world to set up regional locks. For the more niche categories like loli, hypnosis or simulated rape with specific jurisdictional blocks against them? "Sorry, too small, the bean counters have determined that the return on investment of such a compliance system isn't there, so worldwide blanket ban it is in order to pad our margins. What are you gonna do about it? We have a duopoly on global transactions, and you can't really criticise us for it without looking like a pervert."