Cold blooded killers aren't necessarily psycho and are often well balanced and rational in most facets of their lives.
By definition, is a coldblooded killer a psycho? Or "criminally insane"?
Compare Willy with Joseph Cotten in "Shadow of a doubt." Both see a division in mankind such that that they have no doubts (no conscience) about killing. The fact that Willy isn't drooling, etc, is irrelevant. All of Hitch's killers were just as casual and righteous about killing, as well as were undetectable on the surface. The motivations (political, money, family upbringing, etc) don't really make a difference, since not everyone else would behave the same in their situation. Of course, in Willy's case, Hitch is saying "What if you had a nation that channeled it's people's homicidal urges into a national institution?"