futures don't guarantee a profit, only a price. it's up to the farmer to decide whether the price is worth the planting (regardless of profit). and the pricing function only works well in an uncorrupt market.
the problem isn't the existence of the futures markets, but the same kind of over-consolidation that corrupts every laissez faire market, making them inefficient and brittle in the long-run. if regulation encouraged primarily mid-sized firms, rather than a few large ones, we'd have better informed and more efficient markets, albeit less lucrative since the firms wouldn't have undue (read: corrupting) influence.
note that insurance is another alternative to futures or gov guarantees, though i'd question the need to externalize risk, which manifests a critical market-shaping signal.
