In 2012, the last year I can find statistics for, there were 259 justifiable homicides (killing in self defense) and 548 accidental shooting deaths. There is a consistent pattern of 2 accidental shooting deaths per each justifiable self defense killing over the years I can easily find statistics for. And that doesn't take into account the leading cause of death by handguns, which is suicide.
By my reasoning I am twice as likely to accidentally kill an innocent person than I would be to actually stop a criminal dead in his tracks. And without a gun in my possession, I am highly unlikely to become one of the 8000+ people who shoot themselves to death on purpose, which might become a consideration if I shot an innocent bystander to death.