1. Excellent point to raise. Remember total sales is not the same as net profits. After seed, spray, machinery, and loans are paid for, most farmers scrape for cash on the average year. Two choice quotes. My late cousin used to say, "Farming is the business of losing money as slowly as possible," which rang true with the rest of the very agrarian clan, and another saying, "You can tell how good a farmer's day job is by the number of cows he has". Midwestern dairy farms are notoriously unprofitable and probably less dependable than playing Blackjack.
2. Although most people think this, its actually false. True free markets would be better because less expensive commodities from abroad traded for the things a country can best produce locally profits both trade partners. However most countries are still protectionist, particularly with regards to food, because of the political or even military power that arises when peasants revolt. The semi-automatic rifle is the new billhook, and in the democracies they can all vote. In countries with very large numbers of small farmers inefficiently producing small surpluses, leaders have to tread lightly.
3. Mao did this to China and caused the largest artificial famine in history. A lot of poor nations grow higher-value fruits and vegetables specifically for export to wealthy nations (Chile, Argentina), and the people have less food for it. However they do have money, and getting farmers from cash-poor subsistance to cash crops is the fastest way to improve overall farm productivity. Strawberries from a province pay for gravel roads to the strawberry fields and a highway to the village, which then gets used by the staple crop-carrying trucks to get to market. Improving infrastructure is key to improving nutrition in many places around the world, not an actual lack of food itself.
4. Those scientists are Marxist hacks trying to produce global communism, don't listen to them. People can live just fine off really heavy beer and vitamins.