How is either worse than being dependent on foreign workers?
1. Believe it or not, we have very tight controls on the produce that is grown in this country. The standards for food produced in many other countries are not as stringent.
2. Like with everything else it is beneficial to produce commodities here because of residual benefits such as equipment sales, fertilizer and soil conditioner sales.
3. The initial revenue from the sales of these commodities stays here, unless the fields are owned by foreign investors.
4. If we are dependent on foreign countries for our food, geo-political decisions can be influenced due to that dependence, much like it is with oil.
There are I'm sure many other reasons.