The most important debate point on the safety of genetically-modified foods is the nature of the sources. Most of the anti-GM voices from from fringe groups and untested theories; many of them ignore the real sciences in favor of loud, propagandized scare tactics. Most arguments against GM foods are based in guilt-by-association; if the food comes from Monsanto, for example, the food is bad because Monsanto created Agent Orange. The two are completely unrelated, but it is easy to scare people with association tactics that have no bearing on fact. While is is a mistake to dismiss claims simply because they originate from fringe-science proponents who practice deliberately faulty and dishonest experiments, the source should always be considered.
Another point in favor is that there is no known correlation between GM foods and sickness. Despite tests that claim otherwise, millions of people consume GM foods every day without any adverse reaction; anecdotal claims, such as "I ate Monsanto corn and then I got cancer!" cannot be verified as causation. Millions of people eat GM foods; millions of people also get cancer, and have since long before GM foods existed. There is no correlation and so sickness cannot be verified as caused by GM foods.
Finally, the most important argument for GM foods is that they offer a method of increasing food production in poor and famine-stricken areas. Millions of people around the world die because they cannot afford or harvest enough food to survive; with GM crops resistant to disease and climate, food production can be increased in those areas. Millions of lives can be saved if foods are modified to grow and survive in harsh climates; those lives will be lost, as they have been for centuries, if GM foods are prevented.