There are various reasons why charging for parking at hospitals is a bad thing.

Imagine rushing your wife in in the middle of labour and:

1. forgetting your wallet
2. finding that you don't have any change
3. the only parking space is 10 minutes walk away from the entrace (no handy trolleys to like at the airport!)
4. the birth takes 18 hours, you come out to find your car towed/clamped and have to deal with getting it back before you have to pick her and the baby up.

You say that poor people don't drive, but they certainly get people to drive them to visit people at the hospital. them and the elderly. how nice for the person ferrying the visitor to have to pick up the tab for parking to add to their good deed!

There are dozens of better ways to generate revenue than parking and they should all be kept away from the hospital.