GM = Genetically Modified
Certain crops, like some strains of corn, have been modified to produce the toxins that harm the pests that try to eat those crops - like a genetically built in pesticide; or modified genetically to produce substances that make some pesticides more effective.
The arguments center around whether or not the substances the GM strains produce, or the level of such substances that GM strains produce, are harmful to humans or not.
Not according to this article.
To date the industry has always argued that if these toxins were eaten by animals or humans they would be destroyed in the gut and pass out of the body, thus causing no harm.
Whether there are harmful levels, and a contention that the toxins are destroyed in the gut are two different arguments.