Last night I heard an interview with Craig Venter where the interviewer used the term "playing god", or something similar several times to to characterize the arguments she assumed that some others might be making against this research. Venter actually corrected her at one point when she misquoted one of the commenters -- in this case a representative of the Vatican. It sounded to me as though the "playing god" expression was being used more by the proponents of this kind of research rather than the ones raising objections or concerns themselves. I think that the expression was being attributed to people who weren't raising that specious issue in the first place.

Still, I don't know why the expression,"playing god", whatever it might mean,is "dangerous" unless you're concerned that the uneducated masses might be stirred to some undesirable action as a result of hearing it.

Incidently, stem-cell research has high potential but is also highly speculative. Similarly, gene therapy (using viruses to deliver gene fixes into the body of cells) was and is considered to have enormous potential with very similar hype to stem-cells. But after 35 years and billions of dollars of work, the the actual number of people who have been helped is very small.