Another practical benefit is catharsis. People will suppress their urge to murder and riot if they know they can do it with impunity once in a while, and the unlucky victim in this particular town was far from sympathetic; we got a sense that nobody was very sorry to see her die.
Throughout history, the unpopular elements of society were blamed for its ills. The Salem witch hunts had less to do with any pacts with the devil than with some people with desirable property being resented by people who wanted it, and a witch hunt is a swell opportunity to redistribute property and get rid of some people who aren't exactly beloved anyway.
This was published in 1948 (not long after World War II and not long before the Korean War) against the backdrop of the Red Scare, the scapegoating of Communists for various real and imagined problems. If you wanted someone out of the way, insinuating that he was a commie was a lot less risky than, say, punching him in the nose or taking him to court.