Please keep in mind that humans have been conducting genetic engineering via selective breeding for thousands of years. All of the food most people eat is a result of being heavily modified from its original, undomesticated form. Those breeding techniques have turned wild grasses into wheat, teosinte into corn, and invented the banana which is unlike the wild fruit it is based on. Those same techniques have made drastic changes in domestic animals too like turning wolves into chihuahuas. And in each of those examples many unwanted, unpredictable, weirdly recessive traits popped up that had detrimental effects that could not be bred out for untold generations if at all.
With modern genetic engineering the changes made to the target DNA are in a very specific place and add a single very specific gene. Scientists aren't also randomly adding thousands of other genes with unknown effects or unknown recessive traits at the same time, which is what traditional breeding does. That isn't to say that an unexpected characteristic never happens, it can, it does. If undesirable, it can be removed or just not added in another lineage or inserted in a different place on the DNA which might fix the problem -- the point is that geneticists are usually only effecting one small part of the organism's genome and it doesn't take thousands of generations to correct errors.
There are more than 6 billion people on Earth right now. That number could be as high as 10 billion in twenty years, maybe sooner. Suitable agricultural land has been decreasing and will probably continue to decrease from urban expansion and fresh water unavailability. Productivity must improve and GMO crops will be a major part of what makes that possible.
None of this means to be credulous about food. If the idea of GMO foods makes someone uneasy, I can sympathize with that. Really I can. That can be a good motivation to continue looking into things and promote deeper understanding. Perhaps good studies will find serious previously unknown problems or uncover a corporation brushing bad data under a rug. Well, let's look into things and if we can put together good empirical data that suggests change is required, then let's make the needed changes. Evidence based reason will serve us better than hyperbole or ideological hysteria.