Definitely there is a risk to genetically modify humans. First of all, it is not fully understood what are the full impacts of a body when it has genetically modified cells. Would it mutate? Maybe in the future, if genetically modified humans are legally accepted in the society, we would see the results.
This theory can be seen in plants. The maize plant for example, did not look like what we have now in the present time. It was a different kind of crop back then.
Once we took the genes and modified it in some way, nowadays we have the modern maize plant. Imagine what it could do humans. Imagine one species of the world taking over this program. If that country was North Korea and one day, the genetically modified humans to become half machines and half genetically modified freak, what chaos it would do to the world.
However, as we can see from the corn, the evolution of such corn is actually of great benefits, nowadays we get to eat corn that has lots of flesh and it gives farmers greater yield. If imagine, we could modify humans to have less sickness and the way to really cure cancer, AIDS and some other critical illness is through genetic modification of the human genome, it would create a world that is safer in some ways.
Imagine being able to manipulate the gene that is responsible for crime then we would be able to eliminate most of the different type of crimes.
To every project, there will be the dark sides as humans always have this sadistic part of themselves that would try to manipulate their minds to trying out something that is different. If genetic modification was available at the time Hitler ruled Germany , imagine what he would have done to those poor souls in the name of world domination.