Genetic engineering is simply a tool. A particularly malicious individual with an absurd amount of independent resources, ingenuity, and time on eir hands could use it to make something dangerous - but such a comic book supervillain aspirant could be far more effectively evil simply by making a lot of bombs and using them on densely-populated areas.
In the non-comic book world where we live, genetic engineering is done in a veritable regulatory straightjacket. Development of products for human consumption and/or those that will have contact with non-modified organisms must be exhaustively evaluated for risk potential and its expected benefits justified before the research even gets funded, in most if not all cases.
So, no green goo, and no, you should not be afraid. (Interested in the regulatory practices that keep somewhat bullying-inclined corporations such as Monsanto in check, perhaps, but that has little to do with genetic engineering and much to do with corporate politics and asshattery.)
I was raised to believe that genetically-modified foods are unhealthy to eat and bad for the environment, and given a variety of reasons for this, some of which I now recognize as blatantly false (e.g., human genetic code is isomorphic to fundamental physical law), and a few of which still seem sort of plausible.
Because of this history, I need to anchor my credence heavily downward from my sense of plausibility.
The major reasons I see to believe that GMOs are safe are:
The major reason I see to believe that GMOs are dangerous is:
So: green goo, yes or no?