My professor in plant genetics at OSU had an question to make us think about this. Why are some folks kept so poor they can't afford to devote some ground to growing vegetables to go with their grains for needed vitamins? Or afford to buy a few vegetables to add to their meals?
Edit: That said I think they should release the rice. I don't think it's harmful and people need it. But I do think we shouldn't have people so poor in this world that they can't have a few carrots or a tomato plant. Does this economic system of disproportionate poverty subsidize my lifestyle in the U.S.? I also think we should carefully think before we release such technologies, though this one has probably been considered long enough.
Sometimes the problem is cultural. If the prevailing culture of the area is that grains are the best food to grow, and that leafy greens are only fed to animals, then people will grow and eat primarily grains.
There was an article put out by Heifer International about that once. I remember that part of it included an interview with an Ethiopian woman who had gotten some cooking and nutrition classes from Heifer, in addition to garden seeds. She said she honestly hadn't known that greens were good for people, so she had been planting millet in her garden and nothing else. After the training, she added greens and other vegetables, and her kids grew healthier, with the same amount of land.
I've run into this in varying degrees, in all sorts of places, including the US. I have no idea how much of a factor it is worldwide, but it is definitely a factor.