Websites aren't accountable for user content because of the DCMA and Safe harbor laws protecting them from the risk of what users post [1]. Gun manufacturers are protected from liability by the PLCAA [2]. Police aren't held accountable because of qualified immunity [3].
What i'm saying is no such protections exist for financial transaction that occur on a network. Infact, the opposite exists, laws exist (called Know Your Customer [4]) that specifically hold financial networks (like Visa and Mastercard) liable for allowing transactions related to fraud, money laundering or other high risk transactions like gambling and adult entertainment.