A quote embedded in an article on Genetically Modified Foods from truthout.org titled Europe's Secret Plan to Boost GM Crop Production:

'GM crops do not increase yields. Scientists have found genetically engineered insecticide in crops can leak and kill beneficial soil fungi.'
Peter Melchett, Soil Association

* I don't know the Soil Association from the full-contact tiddly-winks association. Let's assume Mr. Metchett is legit for now.

So why do farmers use GMO if the seed is more expensive and the yield is lower? That's crazy! ;^)

So here's the missing variable, as best I can guess. GMO makes farming easier. That is, one farmer can plant more acres which manage to take care of themselves. If I only need to spend half the time looking over each acre to ensure there's no weed issue, bug infestation, or disease, I can manage twice the acreage of the crop. If each acre drops 10%, I still likely come out ahead, even with the extra price in seed.

I'm not saying GMO is good, but I am saying there's likely a benefit convincing farmers to use them beyond good lobbying and marketing.