Merchant banks already do exactly this. There is no shortage of banks working with the adult industry, just higher transaction fees and other stipulations.

>aligned with banks doing risk control

This goes beyond risk control. Insurance has had this figured out for a long time. You can model the risk of porn chargebacks and charge fees accordingly that cover the increased risk of chargeback. Bank behavior towards adult entertainment is a reflection of prevailing attitude of society in which we live, which is frequently quite opposed to sex work. It's not a question of banks demanding much higher feels for legal adult services, they don't want them.

and they often don't, markets are not perfect rational actors