I agree with you and you give the only (in my opinion) really good cause why to become a vegetarian. (And I HAVE studied economics at university level....)
But, It still doesn't change the biological "fact" that both you and me "geneticly" are all eaters (It's true even if you don't want it to be...)
And the big problem when it comes to starvation isn't the meat eaters but instead the population surplus (or growth). The starvation is instead the symptom. THE PROBLEM IS THE POPULATION GROWTH. It's my, and I would believe also the most economists, opinion that you should do something about why we have a problem (not about the symptom). Stop eating meat will not help in the long run.
You should also bear in mind that the poorest countries partly are poor (and have starvation) because of them fighting each other (Etiopia and Eritrea).
And cultivated soil really need to rest every 3-5 years, in order to not "drain out" (from nutrients), and why not then have animals grazing there during that rest. One of the problems with the cultivated soils today are that it many times get drained out. Having cows grazing there every third year would be the most natural way to manure.
But as I said you have a good point in that we should start thinking about things like that,but not only starvation. In my opinion it's more important to keeping the whole environment healthy if we would like to survive in the long run. Draining out the earth, will feed for now, but not in the long run.