Because we save far more patients than we kill.
Firearms are entirely analogous.
Firearms, like physicians, prevent far more deaths than they cause. That means decreasing the number of firearms would actually cause an increase in violent crime and deaths from firearms. This inverse relationship between the number of firearms in the hands of the public and the amount of violent crime has, in fact, been proven beyond any reasonable doubt. History supports the inverse firearm-crime relationship. Half a century of strict controls on pistols has ended, perversely, with a far greater use of this class of weapons in crime than ever before.