What is wrong with genetically modified food?
It depends on the food.
There is nothing inherently wrong with GM food, however as it is such new technology with massive numbers of restraints on research and development, there could be some unexpected consequences of eating GM crops.
As a general, more practical piece of advice. If you are considering just buying and consuming GM products from a market, the regulations in the USA and the U.K are so high that I would trust that they are entirely safe for consumption.
There are people who say that the crops are dangerous, but often with only anecdotal evidence. Personally I categorise these people with the kind who say vaccines make people autistic.