To get approval for a gmo, corporations like Monsanto have to submit 2 reports to the FDA saying the thing is better. Nobody cares if they (as is done) don't publish 5 or 10 unfavourable reports. That passes for "science." It's worth noting that approving GMOs as essentially the same as normal foods was done by an ex-Monsanto head of FDA against the advice of FDA Scientists. What do they know?
The soil degredation evident over 5 - 10 years with monoculture GMO crops is evidence that they're not the panacea they're cracked up to be. Instead of balanced natural soil diversity, repeated ploughing & spraying leaves the soil impoverished, the farmers with the expense of weedkillers, fungicides, pesticides, fertilisers and the food poisoned; the essential microbes & fungi in the soil are wiped out,. & worms greatly diminished. In some places, the workers on the breadline end up poisoned too, but have no choice but to continue.
Are they harmful to humans? Physically, I don't know, but I don't like where some genes inserted in foods are said to come from.
Economically, very often. All that Amazon rain forest cleared for GMO Soy & Corn has not brought wealth to the locals, but it degrades by the year.