you have protection against shady merchants by initiating chargebacks.
Humour me - how would you be at risk of charge back from a bitcoin merchant? Indeed, the lack of charge back may be why porn sites are not head over heels to accept bitcoin.
You aren't. You have protection against a shady merchant as a consumer when paying with a credit card as you can initiate a chargeback if you're not happy with what you received. Without a signature attached to a sale (either at the point of sale, such as in a retail store, or upon delivery of a physical item), it is very easy to just chargeback an item in the first 6 months after you've purchased it. With bitcoin, the merchant has all the power once you've given the merchant your bitcoins.
Porn sites (and any site selling things without a required signature or proof of delivery) would
love to not have to worry about chargebacks from upset customers, or from customers whose kids 'borrowed' their credit cards. The trouble is, it's a pain in the butt to use bitcoins as a consumer currently, and it's a pain in the butt to accept them currently and then convert them into a usable currency.
Further, in a business like porn, your costs are in customer acquisition. If you can solve the customer acquisition problem, the 3% that credit cards take don't really matter compared to how important it is to make the payment process easy for the customer.
