You're neglecting the effort needed to find the keys. Suppose you spend all day every day checking every car for miles around searching for keys left in them. That's your occupation.

Either:

A) You're already a criminal doing it for the money or

B) You're just trying to help people and not doing it for the money.

Person B probably doesn't exist. So you're probably already A, a criminal and you don't care if people think you're immoral.