Cases like the FetLife are illustrative. You can also look into f-list, a furry website which ultimately had to decide not to take any payments when every major processor rejected them. The key point is that companies are required to distinguish between "pornographic" and "obscene" content using a vague case-by-case smell test. So you sit down with a lawyer and kinda guess what's OK and what isn't and cross your fingers the credit card companies swallow it. That's exactly how this story was resolved. You can learn more about the law yourself by looking at an example ToS from Square and some guides to federal obscenity law.
https://www.justice.gov/criminal-ceos/citizens-guide-us-fede...
F-list/e621 was also a massive walking copyright violation (still is.)
I'm not implying that the are trying to cover something up, but it just seems absurd to me that a payment company may be liable for what its customer are doing, and I would like some clear, circumstantial evidence of that.
The laws you are referring to prosecute whoever detains, distributes, sells, imports, mails, transfers obscene material.
However I cannot see how payments providers can be liable, can you produce some evidence in this direction?
I am not a lawyer, but it seems to me that the payment provider is no more guilty that the electric company powering the servers.