“... and leaving a motor vehicle unattended ...”
He left the keys in the ignition. It sounds like a reasonable law”
It sounds like a bullshit law. How about arresting you because you left your front door unlocked when you left home this morning? After all, you made it easy for a thief to get in to your house and steal things, perhaps even your cutlery from the kitchen which they could use to commit mayhem.
I tend to be pretty much a libertarian on most things. A motor vehicle operated on a public way isn’t one of them. The problem is the potential for harm to third parties. Tort law is inadequate in addressing this issue, since the potential harm from motor vehicle accident is much, much greater than the potential recovery from a lot of owners and operators.
By your logic we might as well not have speed limits and drunk driving laws.