This is because the private sector can't (for the most part) coerce you to deal with them. If the government can keep a lid on external costs, the private sector has to create value people want or they lose money and go away.

The government can force you to give them your money and obey their laws. This is what makes them uniquely powerful and dangerous. In a democracy they do have to get your vote once in a while, but that's within a framework they mostly create and police, with extremely high barriers to entry and very little reward for doing "the right thing".

It baffles and saddens me that otherwise thinking people can be so eager to hand power and authority to the government. I understand that -- after a lot of thought and reading and with much reluctance -- one could conclude that the government should be given a particular power because the alternatives are worse.