Dictating what categories are not legitimate reasons for rejecting someone is not the same as "you have to accept everyone!" Obviously, PayPal should be allowed to reject actual criminal enterprises, for example. But there is nothing illegal about VPNs that protect your anonymity.

Besides, I think it's clear that any legislation that disallowed payment processors from discriminating against businesses would also have to give them legal protection in the case that said business end up being sued.