As a farmer there have been times when I have been peeved with the price I've got at the farm gate and then seen what the price is at the supermarket. However, I also have some limited business experience in the retail side and understand the huge overheads that are required to manage the retail operations offered by the supermarkets. 

Supermarkets, like farmers, need to be profitable otherwise they stop functioning. No supermarkets would actually make it harder for farmers to sell their products and produce prices would rise due to reduced efficiency of getting the produce from farm to fork.

There are very few companies/people who would be willing to operate a business with only a 2% profit margin!