You can still buy adult web site memberships with Visa. Just not with PayPal. I think the difference is the higher fees and such they charge for Visa merchant accounts. They're more willing to take on the risk of chargebacks. IOW, the very thing we like about PayPal - that it's a way for the "little guy" to accept credit card payments - is what Visa doesn't like. They don't make enough money off PayPal transactions to make it worth their while, given the risk.