Posted partially in response to this thread yesterday. Note that nearly everyone with any actual expertise in that thread is pro-GMO. Many of them are at least neutral on Monsanto as well, because some of the allegations made against it are either false or exaggerated.
Totally beside the point of whether GMOs are a net positive or negative, people have a right to know what they're purchasing and ingesting. Information is a form of currency, and to say that this information is inherently dangerous (as is the immediate implication from companies fighting mandatory labeling laws), while the product itself is not, is very suspect. Free information is among our most sacred rights. I think we would see less of an uproar if the companies (Monsanto in particular) that produce GMOs weren't so combative about letting people know what it is they're eating. Why hide what doesn't need to be hidden (especially at great cost)?