They've slipped in because that's where the research is pointing, after decades of anecdotes. One of the main instruments for diagnosing psychopathy is the HARE checklist, as in Robert D. Hare; guess what Hare's latest book is called? _Snakes in Suits: When Psychopaths Go to Work_. Yeah.
(I could finish by accusing you of baselessly accusing your opponents of twisting psychology to fit one's worldview, but I don't think most people would appreciate the irony.)