Your core argument is ironic: "The world is really complex, so we can't effectively model it. Therefore we should just use the simply model where there only one approach to solving problems."

One clear example of positive government regulation are rules against mercury pollution. The EPA did a clear cost analysis calculation and found that the lost IQ of children is worth more than the benefit that the company get for polluting the enviroment with mercury.

Lead poisiong is another example. Rules to cut it back might even have reduced crime by a large margin.

It's very hard to argue that allowing companies to pollute as much as their wish leads to optimal results.