Poor farmers know about vegetables
Rather than addressing the larger issue of the merits of golden rice, I want to pick on a comment that Johnson makes near the end of the article. On the topic of alternatives to golden rice, he says:
Are there other fixes? Yep, you could give people pills, or convince them to grow (and eat) more vegetables.
The idea that poor farmers would need to be "convinced" to grow more vegetables gets things exactly backwards. It's true that poor farmers end up with deficiencies of nutrients like vitamin A because their diets contain too much cheap calories like white rice and not enough vegetables. But that's not because these farmers don't know about the importance of eating vegetables. Their problem isn't that they need convincing. The problem is that economic pressures prevent them from growing a diversity of crops.
Traditionally, farmers in most parts of the world grew plenty of vegetables -- sometimes in among traditional varieties of rice, corn, and other carbohydrate staples. The economic pressures that shifted farmers away from this system and toward monocropping staples are complex, and vary from region to region. They involve some combination of tax policy, farm subsidies, changing domestic and international market conditions, loss of land rights, population growth, and ecological degradation. Poor farmers would love to grow more vegetables if they could, but it's not economically feasible.
What poor farmers need is not "convincing" to grow more vegetables, but policy and market changes to make it possible for them to do so. This is the core of the critical view on golden rice. Malnutrition arises from policy systems that are tilted against the poor, and so it seems to make more sense to fix those policy systems rather than finding a technological band-aid for the worst effects.