Hmm. I think they have the right to decide not to buy a product, yes -- but the government historically only steps in and requires very specific labeling for products proven to be dangerous/controversial. Basically, this is saying to an impressionable public: "this product is on a health level with cigarettes." How? They're trying to protect profits that will almost assuredly go down due to consumer ignorance. Studies and surveys have shown that labeling simply will lead to lower sales of GMOs, because the public is brainwashed to be anti-science and anti-corporation. That seems reason enough to me to combat mandatory labeling. If this labeling business hadn't already been associated with negativity -- I would be all for it. Why not know exactly what's in your food, after all (although the average person has no idea what to do with that information anyway). However, there's no way to implement this policy now without it reflecting badly on all genetically modified foods. (Incidentally, I dislike Whole Foods as much as everyone else seems to dislike Monsanto, and they're the ones spearheading labeling to score points with their consumer base.)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.