Some good thoughts there.

Also people need to remember that gathering and preparing most plants (aside from berry plants) require more energy and calories used then the plants return to you.

If you were ever in the situation where your very survival depended on eating edible plants then you better hope that a) there is a lot of the plants in your immediate area to make it worthwhile and 2) that you have some other method of prolonging your survival such as obtaining wild game and fish by various other methods.