Conservatives have long argued unions don’t belong in government. On Sunday night Chicago Teacher’s Union (CTU) President Karen Lewis demonstrated why. She told reporters her union turned down Mayor Rahm Emanuel’s proposed 16 percent raise because “Our members are not happy. They want to know if there is anything more they can get.“

This despite the fact that Chicago teachers enjoy the highest average pay of any school district in the nation ($76,000 a year, plus benefits). Chicago also has a 40 percent dropout rate. Mayor Emanuel proposed basing promotions and layoffs on performance, rewarding good teachers and removing bad ones.

The CTU said no and went on strike. They wanted an across-the-board 30 percent raise instead. Emanuel offered the union most of what it wanted: a 16 percent raise over four years (with no merit pay) and watered-down evaluations that would make it harder — but not impossible — to fire bad teachers. On Sunday the union refused again.

Many commentators have excoriated the union for putting its interests ahead of the well-being of 350,000 children. These criticisms miss the point — the union is only doing its job. Unions exist to get more for their members. No union would give up its members’ job guarantees to benefit others. Unions act in their self-interest, just like everyone else.

In the private sector, competition forces unions to be reasonable. If they ask for too much, they will bankrupt their employer. That’s why unions rarely raise wages when they organize firms. They do not want to wind up like GM, US Airways, or Bethlehem Steel.

The government, however, has few competitors. When the CTU strikes, the city’s children go uneducated. This monopoly gives government unions enormous leverage. Of course they take full advantage of it. The problem is the laws allowing unions to shut down schools in the first place.

The government exists to serve the common good. Collective bargaining hijacks government, making it put unions’ interests first. This is why collective bargaining has no place in government. No one put it better than President Franklin D. Roosevelt:

The process of collective bargaining, as usually understood, cannot be transplanted into the public service. . . . Since their own services have to do with the functioning of the Government, a strike of public employees manifests nothing less than an intent on their part to prevent or obstruct the operations of Government until their demands are satisfied. Such action, looking toward the paralysis of Government by those who have sworn to support it, is unthinkable and intolerable.

Why should the law empower Karen Lewis to find out if there is anything more she can get?