If breathing became a problem due to car exhaust, that would simply present a marketing opportunity for manufacturers to make cars that pollute less. Consumers would demand and purchase these cars to do their part to limit pollution, just like they do now. All without any need for government regulation, incompetent or otherwise.
This is demonstrably false. I am old enough to remember living in places where pollution was bad--air quality in the urban US is substantially better now than it was when I was a kid. See http://www.esf.edu/cue/documen...>here.
Air quality is terrible in many places outside the US, notably in China and in India. I have experienced the air in Beijing--sometimes you cannot even see across the street. You can argue that China does not have a free enough market to encourage clean air vehicles. But you cannot argue the case in India: their market is arguably freer than ours (e.g., they have weak automobile safety requirements). So why don't people buy vehicles with better emissions in India? Because there's no incentive. Fuel-efficient non-polluting vehicles are more expensive, and your purchase alone makes almost no difference. This is a classic case of he tragedy of he commons--the commons here being air.
I am going to charitably assume that you are not a troll or shill, so I'm going to point out that your ad hominem style of argument is counterproductive. If you really care about your point, and you think that it is true, back it up with facts and reasoned argument. Slashdot is today is not the Slashdot of old, but there are enough of us still around whose beliefs are based on facts that a good argument might actually change our minds.