Not that relevant, this happens to a lot of sex-work oriented platforms. Payment processors often discriminate or demand heavy censorship/arbitrary rules from these platforms.
Different industries have different fraud rates and different legal difficulties around the globe. It might not be a good enough reason from your perspective to blanket ban them, but exclusion based on different legal overhead or risk profile is not the same as arbitrary rules or censorship.
I wonder if there is anything to the trope, that when the adult video payment eventually shows up on a married couple’s credit card bill, the spouse who signed up for a heftily expensive subscription will claim that their credit card must have been stolen.
Thus they will demand the charge to be reverted and thus, many charges being disputed simply because of people’s prudishness. And then porn site operators have high fraud rates. I wonder if they are also more liable to become victims of card testing.
I don't know if we can say they are more or less likely to be victims of card stealing, but that there are a higher number of reversed charges unquestionably true. Had huge problems with that before ccbill. Even after, there were still a higher than normal number of issues.
I think honest people would concede that there are many, many legit issues around chargebacks. But if it's about money, then just say it's about money and everyone can sit down and go to work on finding methods of reducing chargebacks that actually work.
The political pressure (on crypto and banking) is also because of fraud. If you are transferring money via a blockchain with no KYC, it's going to be hard to get a legitimate banking partner to be happy with that.
Now when you say 'but it's only going to be used by the sex industry', you're adding another area of high fraud on top. It's hardly surprising that financial companies want nothing to do with two high-risk sectors sandwiched on top of each other.
Just look at Patreon and their continued stuggle with NSFW artists. I briefly worked on a similar smaller site that allows for artists drawing explicit things, and our payment processor would threaten us weekly to cut us off for arbitrary reasons. The chargeback/fraud rate did not differ based on the user drawing explicit content or not.