There are more than a few members of the public at large that are too unstable or emotionally disturbed to have any business carrying a gun, or being anywhere near them for that matter. You know the type, we all do.
To apply that same thought here, if one can say that there is a certain percentage of the general population that shouldn't posess guns, it isn't a stretch to imagine that there could well be a certain percentage of the LEO population that could fall within that particular group, since they all start out as members of the public at large and, except for their career choice, would still be.
I have known many civilian gun owners and LEO's over the years. In both cases the vast majority were completely responsible types that you would not give a second thought to their having a gun. Unfortunately i have also met more than a few civilians, and at least one LEO, that had no business at all around firearms. I am reminded of that old saying about the bad apple and the barrel. It's a pity that there's always going to be one or two in any given group.