All foods have been “genetically modified” over history. Before we could raise plants in agriculture, we had to domesticate them from their wild ancestors. (Compare corn to teosinte, its wild ancestor). Now, most of this has been done simply by selective breeding. Genetic engineering is different because we are actually going into these plants’ DNA and modifying it at that level. There is no danger that messing with a food’s DNA will negatively affect our own DNA. They aren’t creating glowing mutant crops that will turn you into an octopus. However, genetic engineering food crops does pose several threats that, while less glamorous, deserve attention (and regulation). For example, a lot of GMO crops are created to be resistant to insects or other pests. But if they become too common, then an insect could develop an immunity. This is the same concern about use of pesticides, and is a natural consequence of any monoculture. Another concern is that GMO crops will interbreed with non-GMO crops in unexpected ways, without human control (such as seeds blowing in the wind). And any crop or food source needs to be tested for human safety.