Sociopath i don't think so. The moment the guy is said to have a justice, it means he has some believes. We just don't know them yet.
But yeah he is the most dispassionated guy by a good margin. But he can still feel emotions. When he didn't manage to capture Ray he was very frustrated and raged against random pirates.
Maybe he thinks serving the WG is the lesser of the two evils and so is doing his job fully without any feelings. It seemed he grew up in poverty and is around the same place as Akainu. So he maybe saw some shit when he was young.
Yet contrary to Akainu he is not impassionated about what he does. He just does it because it is the only way to make the world overall a bit better/not worse, it's how things are, without being blind about other stuffs but not caring at all.