Unions look after unions

I think this post from Megan McArdle stresses an important point that is often forgotten in discussions about unions and unionization, unions are, first and foremost, out to look after the health of the union rather than the workers. Just like the politicians whose main aim is to implement good policy rather than get re-elected probably won't get re-elected, the unions that don't focus first and foremost on sustaining their own existence will probably cease to exist.