You don't need a concealed-carry permit to carry a concealed gun; you just need one to do it LEGALLY. I would venture to guess that a person who carries concealed with the intent of committing murder will not have bothered to get a permit.
My reasoning for keeping a killing machine (it lies around either in a safe or on my person at all times) is because crime happens, and criminals are willing to do things like use force and/or weapons. Police can't be everywhere, and while their response time here is pretty good, it's generally more than enough time for the criminals to do what they want and escape. I'd be happy to go back in time and un-invent guns, but as it stands, I don't see any way to remove all of them from all criminals' hands. So it seems to me the only viable preventive measure is for citizens to defend themselves with the same tools the criminals illegally use to commit their crimes.