A coke is one dollar. So paying 10 cents to get back a missed dollar suddenly makes a whole lot of sense, doesn't it? I know it's not 1:1, but they have the data, and apparently it's still more profitable/preferable for them to have RFID.
Furthermore if McDonald's doesn't want to attract freeloaders, which bring with them all kinds of other risks and cultural issues that might repel actual paying customers, they have that right. They're not a social center.
And don't forget they HAVE THE DATA.
They know how much cups they sell and how much water and soda they dispense. They've done the math. Can we stop pretending we know more about their profit/cost and operations than they do?