Genetically-modified organisms can't be controlled.

Remember Jurassic Park, where the intended control of Nature -- switch-off gene that only produced females -- failed to prevent reproduction in the wild?  Well, as Dr. Malcolm said, "Life finds a way."

GM papaya on the Big Island spreads outside of its area.

GM salmon was shown to be able to mate and pass on genes to wild fish, despite claims that it couldn't happen.

GM corn had cross-pollinated with wild varieties, and maize, spreading its modified genes.

GM canola cross-pollinated with natural, wild canola, spreading its modified genes.

GM rice has spread, globally.

GM wheat in Oregon, has spread its genes to natural varieties -- as we just found out this morning.

And, of course, genetic modifications to make crops pesticide-resistant, has resulted in the natural selection of pesticide-resistant super-weeds.  Face palm.