If you ask some people, they'll tell you that they think it's not only unfair to have mandatory car insurance in the United States, but that it's unconstitutional. This is the reason some people skip out on buying coverage.
There are two basic reasons why people take this viewpoint. The first is that they don't want the government to step in and tell them they have no choice but to buy a specific product. They feel that's the government controlling their personal finances.
The second reason is that people sometimes feel discrimination against the poor is bred by this mandatory coverage. Someone with less money can't afford the coverage and can't legally drive.
Of course, both of these reasons are wrong, because they both stem from the idea that driving is a right, which it is not. It's simply a privilege, something you get to do if you follow the proper steps. If not, there are plenty of other means of transportation. Buying insurance is one of the steps that modern society has agreed upon through the institution of laws. It's easy to think of a driving as a right since it is so common in the modern world, but this simply is not the case.
The point of insurance isn't to discriminate or to force purchases, but to protect other people who are hit by vehicles, causing injuries or damaging property. This protection for the rest of society is why these laws are in place.
If you've been hit by a driver who did not have insurance, you must know what legal steps you need to take.
Source: Auto Insurance, "Why do some people say mandatory auto insurance is unconstitutional?," accessed May 17, 2016