The main risk in "artificial" GMOs are that the evolved species might be a bit too adapted to the environment and start to replace the original and/or destroy species from the old biome (because new toxins kill usefull insect or small bugs, or because its taking to much from the soil thus kill surounding trees and plants...). Other concerns exist (especially when playing around viruses or other self-repliquant organisms).
I had two really long discussions (hours) with a former PhD in genetic, although he did not wrote anything about DNA: he was studying population of plants, insects and sometime cattle. From what i understood, the issue with GMOs is that the change is too fast, and other organisms from the same ecosystem often can't adapt. But this case sometime appear with "natural" settings too. And human exploitation of ressources have the exact same effect, but often without any scientist to limit the damage, as they are called after most of the damage are done.