The AAAS’s take on it (from two years ago) is here. Basically, it’s two main points are the potential for misuse, and who’s responsible if you make a living thing and it goes awry.
If I make a 7’ high robot and it runs amok, there’s no question who the lawyers are going to be calling on. If I make a pollution eating microbe and it evolves to eat everyone’s car tyres, is citing “Darwinism” enough to absolve me of responsibility? Should it be? Am I required to ‘sign’ my creation so it can be traced back to me if found where it shouldn’t be? Am I required to include a ‘killswitch’ for safety purposes? What if my k/s evolves out? Is that my fault? Do I need to monitor my creations genome for potentially harmful drift? Am I then responsible for its ‘maintenance’? What can and can’t I create an organism to do? Might an organism that produces feelings of calm be a good thing? What about one that only does so when I am in the room?
That’s sort of ethical issues being discussed.
(Edit: wow, did that link ever go astray!)