You say erotica, they say pornography. ANYTHING which doesn't agree with their notion of Right is pornography.
Be like me, then. Don't pay their charges. Pay cash, or pay off the card when it comes due. No interest payments, no late fees, no annual fees. If they don't like it, don't use them.It is they that are telling us how to live our lives without sin, at the same time they rob us blind with their over the top charges.
And when people stop using them because they can't buy what they want, they'll back down or go out of business. I use credit cards because they are convenient. When they stop being convenient, they can keep them. When they tell me I cannot buy something because they deemed it obscene, I will cut up my card. If enough people do that, they will rethink their position. Or go out of business.When they start telling you which supermarket to go to because the others don’t pay them enough return for the use of plastic, then it will be too late to shout Big Brother.