The cold, calculating eyes of a robot can never fully be roleplayed out using a human being.
Humans, Tajarans, Skrell, and Unathi are by nature, flawed emotionally. They cannot come to work and separate themselves completely from their job.
An IPC, however, has none of these inhibitors. If, one would say, someone as an IPC was a HoS, They could RP them being completely black and white, and going completely by the regulations.
Here's a thought also; Why is it out of the picture that head IPCs be given a lawset, sort of like a loyalty implant, that keeps them from doing the things that people are afraid of?