Illinois is on the verge of a major gambling expansion, and citizens are being pelted with competing claims. The advocates envision a gusher of jobs and tax revenues. The opponents brace for an epidemic of bankruptcies, crime, divorce and suicide. Which side to believe? Neither. Democratic Gov. Pat Quinn is now considering whether to sign or amend a measure authorizing five new casinos, including one in Chicago, and slot machines at racetracks as well as Chicago airports. The capacity of gambling establishments in Illinois would more than triple. The motive for this sudden interest is economic. Chicago Mayor Rahm Emanuel...