Pre-paid debit cards aren't a solution for many people. Not only they depend on your bank or a third party service that may even charge for them, but they're more traceable than buying stuff on a store. Some people don't even have a bank account, like kids, who now will need to ask their parents to pay for every game individually (or have unrestricted access to their parents card)

You don’t need explicitly Valve-endorsed cards.

I don't think this is your decision what I need. I don't need your endorsement to use what I want.