They have a monopoly on the ability to extract tax payer money unlike private sector unions. If a union decides overreach in the private sector and causes that product to be too expensive consumers can decide they don't want to buy that product anymore. Public sector unions make tax payers pay for their overbloated wages and benefits and they don't have the option to not pay their taxes. They don't have the right to not pay for those services and the union leaders know this and take advantage of it. I guess it just comes down to the fact that I'm not a big fan of extortion.