From the merchant perspective these middlemen can be infuriating. I use Stripe, and I regularly get chargebacks due to "Unauthorized Use of Card" coming from the issuing bank. Stripe will immediately charge $15, which is not refunded regardless of the outcome of the dispute. Then, for the privilege of countering the dispute, I will be charged another $15 which will only be returned if I win.

At that point it is put onto me to prove that the use of the card was authorized (Which is usually practically impossible given the limited info I have about the person and their transaction).

Then at least half of the time I lose and forfeit the full transaction amount in addition to the fees Stripe charged me, having already shipped out a product.

It all gets folded into the cost of doing business, but it infuriates me that I end up on the hook for "unathorized" use of a customer's card. (Scare quotes because usually I suspect it was authorized and they just forgot or got mad about their order)

So it also makes me mad when I hear people say the middlemen earn their cut but handling fraud and security, since they are just passing that cost onto merchants anyway.