There’s an interesting report on Reuters:
UK scientists downplay GMO threat to biodiversity.
Before reading this it had never really occurred to me before that one of the main reasons people object to GM crops is because they are too efficient. Herbicide-tolerant crops mean that most weeds can be killed, and this is seen as bad because no weeds means no spiders and insects which means no birds. But where do you draw the line? Obviously all agricultural advances of the past have affected biodiversity in certain areas. If you object to GM crops on this basis I think that the logical conclusion of your argument is that all agriculture is bad.
But, to be fair, I imagine what they want is a balance. But greater efficiency in crop-growing means less land is required for it, and GM is a step along that road. Do they really want to halt agricultural progress at the current level? Small-scale organic is no answer to the demands of the world population. Rising populations have always been accompanied with rises in the capacity of those populations to feed themselves. This is a defining characteristic of civilization.