Here. In particular see the meta-analysis (4th on the list). For the connection to babies and cuteness see the second to last on the list. To summarize: the fear expression mimics infantile expressions- enlarging the eyes and opening the mouth. The reason for this is that the way babies look elicits a caring and protection response in other people. Psychopathy is, at least partly, a dysfunction in processing fear expressions. There is decreased amygdala activity in response to distress expressions among psychopaths relative to control groups. Thus, finding babies disgusting suggests some pretty serious amygdala dysfunction.

There is no direct evidence that finding cute babies disgusting means you're a psychopath but it suggests that the something pretty abnormal is going on with the person's experience of empathy.

Note that saying someone is a psychopath that doesn't mean he/she has committed any crimes or is particularly damaging to society. Indeed, given some estimations it would be very surprising if there weren't several psychopaths reading Less Wrong. Higher even, since there is some evidence of comorbidity with other conditions that seem to be unusually common here (like ADHD and problems with executive functioning, for example). I guess being called one carries with it some negative social costs. That should have occurred to me and maybe it is reasonable to delete my comment above as result. I honestly just saw the evidence and thought it was an interesting thing to point out- I wasn't being reflective.