So a couple of things:
1. Why can't the bank refuse to process the charge?
2. This seems to be failing, in practice, at dissuading people and making them pay attention to keep a positive balance. At least according to a couple of comments here, there are people who are repeatedly hit by overdraft fees. Is there something better that can be done do solve the actual problem, which is banks having to come up with money to cover these tiny loans?
3. Is there a more proactive way to solve this, such as notifying people (phone, text, push notification, whatever) that their balance is low and they have a recurring charge coming up? Wouldn't that be better for the bank, so that the problem wouldn't happen in the first place?