BeeDubya - states the case very well,
a safe naturally occuring pesticide such as bt may only be useful
for the next 50-100years - until resistance builds up thanks to gm modified crops containing bt.

gm crops didnt become an issue in North America until monarch butterflies started dying because of bt-corn.
Which I believe was approved only for livestock consumption, but later environmental watch dog groups found bt-corn dna turning up in a variety of products such taco shells in the US, and as far as Japan.
Even though farmers were required to keep it out of the human food chain because it was untested - it tended to aggravate human allergies. SInce theres no way to prevent some farmer selling at corn for human consumption the genies out of the bottle.

theres also the fact that simply modifying dna is more like a shot gun approach - its not that accurate and retroviruses lurking on the dna could be modified as well. You cant recall a virus once its out there.

there may well be benefits to some gm crops - such as the yams grown in Africa - that are far more productive in a dry environment so I wouldnt dismiss it entirely. BUt after various scientific failures of the past, ddt, thalidomide, bse (thanks to feeding groundup sheep to cattle) I want to be informed. At the very least gm food should be labeled.

Percy Schmeiser the Saskatchewan farmer battling Monsanto, who sued him for growing gm canola without paying a royalty is a case to watch.
Since agriculture began farmers kept their own seed for next years crop. Now with gm canola seed must be bought each year from Monsanto.
Schmeiser refused to do this and did not grow gm canola although neighbouring farmers did and drove their trucks containing seed (covered only with a tarp) through his land. Neighbouring farmers would notice a plane flying low across their land (without notification or permission) and a week later there was a swath of dead crops. A helicopter would show up and check it. They found out from their Monsanto contact that this is the way they get audited.

MOnsanto sprays a herbicide on a patch and comes back a week later to see if its dead. If it isnt they know the farmer is growing a weed resistant canola.

Even though under Canadian law, one cannot patent a living organism, somehow MOnsantos lawyers won a right to claim that since Monsanto owns the modified gene the plant is a result of the gene etc etc.

its an insidious process, where the company goes out to remote lands and collects seeds from all sorts of crops that have undergone thousands of years of selection. THey make a slight change, patent it.
And then local farmers have to buy seed, and the resulting monoculture leads to loss of diversity - and problems such as the Irish potato blight, and the US corn blight in the 60's and others