One mans "censor" is anothers "brand protection". Given that they are currently allowed and expected to decide who gets to use their payment networks, it seems pretty obvious to me that they won't allow extreme content next to their logos. If you made clear rules that specify when they have to extend service, I'm sure they would love to relinquish that responsibility. Visa has no moral objection to what you do, as long as they make money and aren't exposed to political pressure.

Approximately zero people, reasonable or unreasonable, believe that they payment processor has anything to do with the business. You can see this because whenever a business is caught doing something naughty and people try to cancel it, no one ever says "this is all VISAs fault - they're next!"