The Evolution and Potentially "Extinction" Consequences of Synthetic Biology

In the 1970s, genetic engineering was the hot new technology in which DNA molecules from one organism could be spliced into another organism's DNA. Today, synthetic biology could likewise revolutionize our way of life. But synthetic biology is orders of magnitude beyond genetic engineering because it can create completely novel DNA sequences. By human "intelligent design," synthetic biologists could conceivably create new life-forms previously unknown to this planet. Given our current understanding, it's hard to know whether this is a good or bad thing. But since life-forms--at least the nonsynthetic ones--are typically unpredictable, how can we make sure that synthetic biologists create new life that would be purely beneficial?