I've seen some crazy stuff of FB on this topic. One thing that got me going was the "Monsanto is evil" stuff. For, petes sake what did they ever do to you. So what if they invented GMO's? That don't mean they are out to kill. Monsanto is trying thier hardest to make the world a better place with GMO's that produce better yields and so on. Just think, how in the world would we farmers be able to feed a growing population at over 7 billion already by organic ways of farming?
Actually, Monsanto is quite predatory and treats farmers badly. They've tried to patent tank mixes, they've sued farmers for wind-blown canola self-planting itself, etc.. I dislike them a lot. Of course that doesn't keep me from using Roundup, including on my veggie garden. I may not like Monsanto, but the product works.
When it comes to labelling, I don't think cost is a major issue. They already know what's in the products, and computerized systems make printing one label about the same cost as printing another. I do think people would be unduly frightened by the labels though. Chemical names are scary, no matter how benign the actual chemical is, and as a society we are pretty much scientifically illiterate.
What I would like to see on labelling is a simple "May contain GMO's." That would allow those with medical problems to be aware. Most of the rest of us would just ignore it, just like we ignore the calorie and nutrition information on current labelling.