Easy. He’s a sociopath and is just playing a role. He has no remorse, no emotion, and until now, nobody has called him on it.
It’s not a case of dehumanization to recognize that Gosnell, and others of his kind, aren’t really homo sapiens sapiens. His behavior and attitude are much more like that of homo ergaster ~ a possible predecessor species, but one with no conscience as we would understand it.