The fact of the matter is that just because something is labelled, does not mean it is an informed decision, since the vast majority of the populations scientific literacy is less than zero, and associate gmos with some boogeyman stigma that isn't founded on anything scientific. While we're at it, why don't we put 'contains Cyanide'stickers on apples and 'contains formaldehyde' stickers on pears. There's also a staggering number of people who think organic food is pesticide free and don't realize that the organic food industry is worth billions and has plenty to gain by misleading a gullible public into labelling the boogeyman gmos. There are plenty of reasons to not label them, and corporate lobbying is not the whole story.
There is some serious tin foil hat material around this subject. Multi-billion dollar oil companies couldn't even come close to influencing scientific consensus on climate change yet a bio-tech company worth a tiny fraction of that has somehow managed to buy scientific favour the world over. Give me a break.