Because criminals are by nature lawbreakers and don't care if guns are banned. Gun laws affect only the law-abiding, making them even more vulnerable. Gun control is just a more acceptable term for Victim Disarmament.
Police shoot more innocent people mistakenly, by percentage and sheer number, than civilian gun owners. Police cause more accidental shootings due to bad gun safety practises than civilian gun owners. Since they're such dangerous gun owners, why don't you take away their guns?
Incidentally, nowhere in Doyle's novels will you find the phrase "Elementary my dear Watson"...