The law isn't just to prevent theft, it is to prevent the car rolling away, catching on fire, etc. as well. It IS against the law. If you choose not to cite, that is your choice, but it is an offense and it is an offense for a reason. I am sure these folks feel terrible for what happened, and I don't blame them, but they were at least a small part of the reason. And I'll bet these idiots knew that these folks regularly left the car running outside and took advantage of it as well.