If there's gonna always be 10 or 15 percent of the population who sees it as their civic obligation to steal any unlocked bike they see, then the responsibility shifts to the bike owner himself, to make sure they use some sort of lock, even if not perfect.
Because in way, by creating opportunities for a thief to steal a bike, that person becomes part of the problem.
Gunnery Sergeant Hartman: Private Pyle, if there is one thing in this world that I hate, it is an unlocked footlocker! You know that, don't you?
Private Gomer Pyle: Sir, yes, sir!
Gunnery Sergeant Hartman: If it wasn't for (reproductive organ heads) like you, there wouldn't be any thievery in this world, would there?
Private Gomer Pyle: Sir, no, sir!