I'm interested ...
(Genuinely. I hold fruitarianism to be a higher ethic than veganism but have never explored the practicalities in any detail.)
Facts, figures, sources?
Roughly six decades of life in an agricultural family. It still sometimes surprises me how little most veg*ns know about what it takes to produce enough food to feed a human being. I understand the average joe being ignorant about what it takes to get all that nice prepackaged and processed stuff onto grocery store shelves, but I keep expecting veg*ns to be more informed, especially since you just need a very basic understanding of human history or a very basic understanding of math.
Grains and legumes are high caloric crops. It was the development of grain and legume agriculture that supported the great growth in human population, because one acre of those types of crops produce so many more food calories than other crops.
Corn is one of the highest calories per acre crops, if not the highest. (See this analysis of how many humans could be fed if corn were the only crop:
http://fatknowledge.blogspot.com/2008/11/how-many-people-can-earth-support.html ) If you grow crops that have a lower calorie value per acre, more acres are needed to produce the same number of calories. Very, very basic math.
I guess it depends what subset of fruitarianism one belongs to, whether one will eat grains. So, if one is a fruitarian who is O.K. with eating corn, soybeans and other legumes, wheat and other grains, you would be O.K., as long as you don't object to the plant being "killed" as part of the harvesting process, since it's an annual anyway. (Large scale harvesting of grains, legumes, etc. is simply not feasible without taking out the plant in its entirety.)
I think it would be educational for veg*ns to grow gardens and learn firsthand what it takes to produce their own food.