We assume that the quality of the food meets standards that have been created to protect public health. We believe that the materials the vendor used came to him legally, under laws that protect our environment and the safety of those who produced them. And we are willing to engage in this transaction, not just because it costs us less than it would to produce the goods ourselves, but because we have confidence that the market is embedded in that network of evolving rules that create a just and healthy society. Trade based on real comparative advantage makes sense. Those advantages can be ecological in nature - growing bananas in the Palouse and wheat in the humid tropics simply doesn't work, so an exchange of those goods makes sense.
Comparative advantage can also be technological and organizational.
The fact that we have developed a sophisticated infrastructure around building jet aircraft is a real advantage which would simply be too expensive and difficult for most nations to replicate, so it is reasonable for to produce that commodity for trade purposes. But some trade is based on false comparative advantage. If goods made in other countries are cheaper than those made here because those countries don't protect their environment or use child labor and don't pay living wages, we should not put into place trade rules that allow those products to displace ones made in places where workers and the environment have significantly more protection. The rules of world trade need to be set with reasonable standards for workers, working conditions and environmental protection. Countries should be allowed to set higher standards, but the World Trade Organization should not be allowed to consider such standards to be 'restraints of trade', and should, in fact, encourage them.