It's a stupid test and the whole thing is a false dichotomy.
A socio/psychopath could kill the baby out of a lack of caring for it's life, or he/she could not kill the baby because he/she doesn't care if it grows up to be the next Hitler. They might see it as a waste of time and they also wouldn't want to go to jail to save other people. A socio/psychopath could make either decision.
The empathetic person could make the decision to kill the baby out of love for mankind and for the greater good, but also not kill the baby out of empathy, and the guilt he/she would feel for taking life.
It's stupid to assume that a psychopath would kill the baby and an empath would not. It's the choice that matters in the long run, but when it comes to diagnosing someone as a psychopath then you need to find out the reasons behind the choice.