David Wolfe is right about the mono meals but he is a prick who tries to sell you supplements and other stuff you'll never need.
Maybe give the diet a try to see how you go. There's quite a few books out there that shows fruitarianism to be a sustainable diet including "The china study" and Doug Graham's "80/10/10 diet" loads more of course.
Protein is a bit of a concern for a lot of people but most fruits percentage of protein is between 0.8g and 2.5g. Breast milk has a percentage of 1.8g of protein which is when it is needed most in the development of the child. Protein is a bit of a myth as our cells mostly thrive of sugar. The reason people get candida and diabetes ect is because they are eating to much fat for the insulin to move the Sugar to cells. The fat coats the tissues and cell walls.
As long as you add in some nuts and maybe an avacado one a week you should be fine. Make your own low fat hummus if you're really concerned about protein.