I stay well clear of GMOs for a few reasons.
First, on the topic of world hunger, we can cure it today. We've got all the food we need. But there's no profit in doing that so people starve. To death.
Second, people lie, corporations lie. It's just a fact of life. Let the buyer beware and all that.
By 1 and 2, if Monsanto (the really major player) and ADM are claiming the productivity->world hunger thing, they are trying to distract you. Wouldn't be the first time. No conspiracy theory here, just assuming they are trying to make money and don't want anybody to see the big payoff they're hoping for somewhere down the line.
Third, stockpiling heirlooms? Now why would that be? Unless we consider:
Fourth, when any market comes to be dominated by < 5-6 big players who cannot be controlled by a government, they consolidate to 2-3 and then form monopolies, and extract maximum profit from the market.
Fifth, GMOs are PATENTABLE. A farmer who buys GMO corn is legally forbidden to take some as seed corn, he must get his seed corn every year from the patent holder. Sterility genes now allow GMOs that produce sterile seed.
Sixth, anybody who didn't bother to stockpile non-GMO seed will have no supply except from the GMO source, who, surprise surprise has been stockpiling other non-GMO seed as well, so that
by 3, 4, and 5 and 6 a non-paranoid person may conclude Monsanto, ADM and a couple of others are actively trying to corner the world market on food. Wouldn't be the first time somebody has pulled it off (well, regionally, not worldwide of course).
A non-paranoid person would also believe that the big GMO Corps' explanations for stockpiling is their need for genetic diversity for further research. Plausible, likely true, and wonderfully incomplete. It also allows them to say, "Hey its not my problem if you didn't keep any seed corn, this stuff costs money to keep, of course we have to charge for it -- after we've slipped in the sterility gene."