I don't play the points game, I use a cashback card.

I use a cashback card, because most merchants will charge me the same regardless of payment method, and getting a 4% discount (+ time value of money) is the lowest cost to me. If I use some other payment method, the merchant may keep more of the transaction amount, and that's great for them, but it doesn't improve my customer experience. If interchange fees are strictly capped and cashback cards disappear, I wouldn't be upset; but while they're here, I'm incentivized to use them... following economic incentives while doing economic transactions seems like the right thing to do?