It is one thing to choose to deny payment processing of your own free will, and entirely another to be extorted by the courts into doing so. If Pornhub is acting illegally, it should be shut down. If it isn't, neither payment processors nor anyone else should face legal jeopardy for doing business with a legally operating company.

I would were I to manage a payment company.

I'd want to, but not at the expense of people's freedoms, same as how I wouldn't censor things I didn't like if I were a bookseller or an ISP. If I thought they were involved in something illegal I'd turn the info over to the cops to investigate (I'm not HSBC!), but I'd just have to accept that people are going to do things I don't care for. There are plenty of companies I don't do business with now because I can't support them or what they stand for, but I have that luxury because I don't run a company that is (for some reason) allowed to insert itself in between people's private lawful transactions. I've got no business dictating what other people can or can't spend their money on.