I understand the customer side of the equation because that's the side that matters. I make money when customers feel safe in spending their money with me. Happily, Visa/Mastercard/Paypal assist both us and the customers by providing a trusted, regulated intermediary. We can certainly be ripped off by customers, and sometimes are, but that's our business to manage. If someone should bear the burden here, it should be the person whose enterprise is this, rather than the person who just needs to buy something. The merchant is more equipped to deal with the consequences of trust, in other words, in those cases where the third-party intermediary (visa/mastercard/paypal)'s guarantees aren't sufficient.
I'm not sure what is the point in this discussion when you openly state that only 1 side of the transaction "matters"...?
I make money because I sell a good product, at a good price and I have built up a good reputation over time.
I don't make money because people can throw their credit card at me willynilly without giving a crap if I'm going to rip them off.
As already stated, customer is in a much better equipped to trust a merchant because it is very easy to find feedback on a merchant. Merchants are very poorly equipment to verify trust.
Visa/Mastercard do not "assist" you with chargebacks, it's handled by the individual banks involved.
For example:
I get paid to my Paypal, customer chargesback the payment on the Mastercard issued by Bank of America.
Paypal can then go to BoA (hat in hand) and say "pretty please can you pay us because the products really were shipped here's the proof".... it's solely the discretion of BoA if pay the money...and Paypal is not their customer, the merchant is not their customer so they have no incentive to pay, instead of the side with their own customer almost every time.