While there are international laws regarding trade, other countries may choose to ignore these laws. China is one country that notoriously fails to abide by safety regulations in many industries. If the United States grew and processed all of its own food, it would be safer due to regulation. In addition, it could improve the economy and reduce food costs based on lower tariffs.
The China food scandal has highlighted that it is impossible to control food safety and quality if you grow and process your food in countries that have different standards and different laws. China especially has a long history of providing poor quality and possibly dangerous food to other nations including it's neighbour Japan.
Growing our own food instead of relying on the standards of the countries we import it from makes more sense, but is not foolproof. Obviously it gives us more control over the standard of processing from the beginning to when it lands on our plate, but I think there is still plenty of room for increasing standards.
While I think growing our own food is commendable, I don't think it would provide necessary variety of food or affordable food in the long run. The United States cannot grow common food items as citrus fruits and some vegetables at affordable prices in comparison to cheap labor and farming costs seen abroad.