I've spent plenty of time reading research papers on the effects of GMO's. I work in a lab where we test the effects of pesticides (organic, artificial and genetic alterations of plant defence) on pollinators of crop plants. We work specifically in the field of preventing unsafe pesticides from being licensed in the UK, I feel confident I've got enough background in this issue to speak about it.

Your points about genetic drift are vastly over-stated, these is minimal evidence that this occurs in the field to any significant level. Mainly because outside of monoculture most GMO genes are a hindrance rather than any competitive advantage and even when they are genetic drift is often enough to swamp them (I assume when you said genetic drift you meant gene flow rather than changes within a population due to random sampling.

Transgenic maize has shown to be relatively harmless to a vast swathe of nematodes, true earth worms and a whole host of soil microbe classes. The one example of bt toxin having a harmful effect on NTO's was with the monarch butterfly. One of my colleagues Angharad Gatehouse wrote a rather damning paper on the actual ecology of such a claim (effectively disproving it's legitimacy) in one of the Trends journals (I forget which, it should be easy enough to find on WOS).

While I'd be inclined to agree with you it would be pointless to bother with GMO's in organic farming (mainly because it's such a small niche it would be worthless), when it comes to actually feeding people it's pretty much a no-brainer. It allows for reduced pesticide spraying and novel ways of getting around the lack of iron and vitamin A in the diet of about 1/3rd of the Asian and African populations.