Comment by skybrian

You could think of credit card rewards as a form of price discrimination similar to coupons. Whether you get the higher or lower price depends on what you do. Credit cards with high rewards are discount cards.

There are many ways to pay and they have different discount rates. Some places have a cash discount, for example.

As a "tax," this falls on people who don't shop around for whatever reason. Some of them are wealthy and can't be bothered to play this game. Others might not find playing the game feasible for other reasons.