I don't know about "increasingly." I think there are two places in my area of the city that offer a cash discount. These kinds of tactics really aren't convincing customers to use cash - maybe if they turned it around to "a 3% fee will be added to card transactions" then people would care. Anyway, discounts are enough of a pain that it's not worth the accounting.

Look at your costs, including card transactions fees, and spread that across your pricing. It's no different than pricing in all other business expenses - do you complain you're paying a "toilet tissue tax" because you don't use the toilet when you stop in? Paper products in the bathroom are a cost, and those costs are put into the price everyone pays for a donut.

Now, I'll agree having a minimum plus percentage of every transaction is predatory.