The most important professions in the modern world may be the most reviled: advertiser, salesperson, lawyer, and financial trader. What these professions have in common is extending useful social interactions far beyond the tribe-sized groups we were evolved to inhabit (most often characterized by the Dunbar number). This commonly involves activities that fly in the face of our tribal moral instincts.
Why the focus on advertisers and salespeople? I mean, if you're just talking about extending 'useful' social interactions, policemen do that too. So do company managers and military officers. There are lots of lines of work where people interact with a large number of people on a daily basis. Drug dealers would be another example. Yet such professions need not act in a way that is psychopathic (except maybe drug dealers, but they, too, often build friendships and trust with their clients).
Rationality quotes time!
The usual rules: