Perhaps Prop 37, the ballot initiative that would have required food companies to put a label on packaging if they used GMOs, was poorly constructed. But its defeat is a blip in the arc of history. The power of openness and transparency is a relentless tide that's only getting stronger.
There are reasonable arguments to be made for GMO foods, just as there are reasonable arguments to be made against them. But there's no reasonable argument to be made against letting people know what it is they're eating, so that they can make an informed decision about what to buy and what not to buy.