I think GMO foods are a necessity. At some point it's going to become difficult to feed our populations effectively so we need to create more efficient crops.
That being said I have concerns about the effects on crops down the road. Given that 90% of corn grown (I'm taking this stat from this thread so I won't vouch for it's accuracy) is now controlled by one company and the fact that cross pollination will pass the GMO genes on to other sub species of the same species I think we may be crowding out the diversity of certain foodstuffs. This may not be an issue now, but what happens when some corn plague comes through that just flat out decimates all corn with a certain gene we've introduced that has now been passed on from the 90% to the 10% through natural processes, or when Monsanto goes bankrupt, stops selling seeds but still has all of the patents, or when a "pest" is wiped out as a result killing of some beneficial predator of said pest? These may be unlikely to happen but sometimes a slight risk isn't worth an overwhelming consequence and I can conceive a lot of mini-doomsday scenarios with thinning out the gene pool of portions of the food chain.
When I go to the grocery store I can buy clearly labelled "Organic" apples so why can't I buy "Non-GMO" apples? I wouldn't because I'm cheap, but I should be able to regardless of my perception or understanding of the safety of GMO foods.