I think this is an amazing scientific accomplishment, and despite the risks associated with it I believe humans will benefit greatly from this.
As said in the article, the potential uses of synthetic cells are huge. So many things could change from the use of these cells. While there is certainly a big danger associated with them, there has been danger associated with many scientific advancements. Granted most of those haven't had the potential for an apocalyptic level of destruction like artificial cells do. I think the biggest potential drawback of this would be environmental problems. While the cells themselves can do thing like clean up pollution, they could begin to damage the environment. It would be very difficult to control the spread of said cells, potentially leading to disaster.
I doubt that these can be used as an effective weapon though. They would certainly be potent killers, but as mentioned earlier controlling them would be a huge issue. So you could easily screw yourself over by using them, leading me to doubt their use as a weapon. Though I could easily wrong. This research really could branch out to so many different things from here.
As for the ethical issues, I really don't see the problems with this. They are just cells. It's not like we are artificially constructing a sapient organism. We are using these cells as tools, just like how we use machines as tools. Just because they are biological does not mean they are somehow off-limits, at least to me.
EDIT: This thread isn't even about robots and people are still making robot apocalypse jokes. I am disappointed.