Nina Easton’s latest Fortune column offers some sobering data for union activists:

Among independent voters, who determined the 2008 election and are likely to do so again in 2012, labor support has plunged to 42% from 54% in early 2007. While more than half of all those polled believe unions help lift wages and benefits, they worry that labor agreements hurt workplace productivity, the availability of good jobs, and the ability of U.S. companies to compete internationally.

The biggest kink in relations between the public and unions comes from this fact: For the first time in history, most union workers are in government, not in the private sector. So taxpayers, not shareholders, are the ones footing the costs for generous pay and benefits packages — packages negotiated by legislators with no financial stake but much to gain by securing the political goodwill of union bosses.

Even President Franklin D. Roosevelt recognized this skewed bargaining relationship, writing in 1937 that collective bargaining “cannot be transplanted into the public service … The employer is the whole people.”

The Depression-era President went on to condemn “militant tactics” by government employees. But today’s unions — both public and corporate — are reacting to being under siege by resorting to tactics that only further erode their popularity.