Some of the dangers of GE are largrly imaginary, but there are some valid risks.
One risk is that GE organism might be better than other similar organisms, causing the non-GE organism to become extinct.
Another risk is that the wrong genes may have been combined, producing an organism that is dangerous to humans.
There are other risks that are similar to this, like a virus that is extremely virulent and deadly. However, with the proper precautions taken, and for every new strand of DNA to be tested to make sure it has the correct genes will eliminate most dangers of GE.