More food is produced each year than the global population requires. The reason people still starve and are malnourished are complex, including issues such as transport & infrastructure problems, corruption, lack of storage, lack of hygiene education and so on.
In the developing world, organic farming on many crops increases yields. In hot climates, plants pull their roots up to get the fertilisers and loose the benefits of deeper roots to get water. Reliance on artificial pesticides means that when economic conditions prevent them being bought, natural methods aren't in place (or have been forgotten) and pests run riot ruining crops. Organic methods manage the soil and improve natural fertility.
Eating only non-organic foods here in the developed world won't help those elsewhere in the world that are hungry.
The point on economic conditions changing is not a valid one, you might make the same argument for investing in an a road network or electricity grid, saying that if economic conditions change and fuel is no longer affordable the economy will collapse.
Regarding the point on roots rising to get nutrients from fertilizers in the topsoil - are you sure that's true? There are many negative effects of fertilizers but I don't think that's one of them.
Its also not clear that organic farming requires increased land use. Many people confuse organic farming with traditional farming carried out pre-"green revolution", which is better perhaps termed "low knowledge" farming. To farm organically you don't simply remove the artificial fertilisers and pesticides, you use techniques such as monitored crop rotations, green fertiliser plantings, natural predation and so on.
I don't have much time at the moment, but a quick google instantly brings up [1] and [2] showing examples of models and actual implementations of organic systems that increase rather than decrease yield. A google or pubmed search for organic yields, organic farming, organic developing countries etc. will give you weeks worth of reading on the subject.
My point regarding economic conditions changing is indeed valid. A farm reliant on pesticides may be wiped out entirely by a short, small economic downturn for that farmer which means she cannot buy pesticides for a short while. This leaves the farmer in a much worse position than if they had used free, natural methods and pest management, which may have a lower impact but fail catastrophically much less often. When you're crops are wiped out, it really is often game over. Lets compare that to, say, a investing in a road used to transport the crops to market. The economy falters a little for a year, and there is no money to repair the road, so you can't get to market. You crops survive and have to be thrown away. Next year, or the year after, the economy picks up and the road is repaired. You've had a very hard year or two, but you've still got your crops and you can get back on your feet.
I can't find the study regarding the roots, it was conducted a few years back (I used to run an organic coffee company and took notice of these things), it was a study conducted in Ethiopia by several NGOs and a couple of EU Universities. I'll try and dig it out when I get home tonight and update this post. The roots either tended to grow upwards/owards (closer to ground level, not out of the ground) rather than downwards, or were shorter/fatter due to having the nutrients they needed closer to hand. During dry spells (more common without irrigation) they performed much less well than organic counterparts which could tap into the lowering water levels for longer.
[1] http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjourna...
[2] http://www.sciencedaily.com/releases/2007/07/070711134523.ht...