But we do not live "in general." We live in particulars. And free trade may not be so great in a particular case. An example:
If I had been the king of the United States in 1985, I would have been worried about the fate of Detroit. Yes, the U.S. auto industry has become sclerotic, and things had to change. But I would have worried about the impending death of a great American city. What I would have done is declare a tariff on foreign automobile imports, set high enough in year one to protect Detroit's current sales, and then declining over, perhaps, 20 years, so that at the end there was no tariff at all. This gives the people of the city time to adjust their lives to the new reality. Other Americans would have paid somewhat more for cars during that period, but it would be worth it... to protect the common good of American society.
Of course, I made myself king in the above scenario. An obvious problem is that in reality, once the tariff was established, there would have been intense lobbying to keep it in place. But these practical difficulties are merely indicators that our politics has lost the sense of seeking the common good, and are not a problem with judicious trade regulations themselves.