I guess the question is whether the business they serve is legal. YouTube has some pirated content for sure. The business has rules in place to deal with it, for better or worse, and if someone pays with a credit card to watch something illegal in YT, that doesn’t count as the bank facilitating a crime.
I’m not defending porn as a grand corner of free speech but I don’t like banks deciding who can and cannot be paid.
The counterpoint that a banker would make is that they're forced into this position by Congress, regulators, and prudence.
The alternative that might work is charging businesses fees that vary according to the risk of their transactions being illegal. Which sounds good on paper, but also runs the risk of leaving the bank in the position of making a large amount of fees from illegal activity, which rarely goes over well in court. Better, perhaps, to have a unified fee schedule and just refuse any business that could be unprofitable from liability.
I think the banker would have a strong point here. They're not in a place where these are always easy calls to make - transactions don't come with an evil bit. The constraints placed on them don't leave them a lot of viable choices.
I’m not defending porn as a grand corner of free speech but I don’t like banks deciding who can and cannot be paid.