An Ethical Dilemma

A few weeks before break, my biology class was shown a documentary starring Francis Crick (of Watson and Crick, the duo that proposed the most plausible DNA structure so far), featuring his views on the use of genetic screening, genetic engineering, and so forth. One of Crick's responses, which sums up his stance, was "If we don't play God, who will?" Although I see some knowledge issues in this statement with regard to religion, I couldn't stop thinking about the sentiment. I myself am a subscriber to the natural selection theory, but I wonder, how much are humans a product of their environment anymore? Of course we haven't managed to escape the loop thus far, but scientific advances, specifically in genetics, has made it and issue of increasing importance. Is it ethical to intervene with the delicate design that is DNA when we have no way of knowing the long term repercussions of such actions? At the same time, are the short term benefits of genetic powerhouse crops, and even genetically strong people, more important than potential issues that may or may not occur in the future? Or are we so far into designing our environment to suit us that the time for making decisions is past? Part of what makes this debate a difficult one is the emotionally loaded language that is used to fight it, since quality of life is at stake either way. Nevertheless, I am interested in what you all think, as this is a dilemma that has stumped me for quite a while.