On his daily radio and television shows, Glenn Beck has elevated once-obscure conservative thinkers onto best-seller lists. Recently, he has elevated a 78-year-old liberal academic to celebrity of a different sort, in a way that some say is endangering her life. Frances Fox Piven, a City University of New York professor, has been a primary character in Mr. Beck’s warnings about a progressive take-down of America. Ms. Piven, Mr. Beck says, is responsible for a plan to “intentionally collapse our economic system.” Her name has become a kind of shorthand for “enemy” on Mr. Beck’s Fox News Channel program, which...