What exactly is the moral/ethical problem with a professional athlete taking performance enhancing drugs?
I'm talking about a talented professional who carefully weighs the known risks and side effects of such drugs and decides their use is necessary for him/her in order to be competitive in their sport. Shouldn't this just be a personal decision?
Aspiring beauty queens are allowed to get plastic surgery, and athletes are allowed to get "corrective" laser eye surgery (significantly improving their perfectly normal distance vision)...
I agree with Aaron that a central reason why taking performance enhancing drugs is wrong is that this action violates existing rules and so undermines standards of fairness that are so important to sport and to the enjoyment of sport by others. With respect to the content of these rules, I imagine that an historian of sports would have an interesting story to tell about the differing conceptions of competition that have been in place at various times and places, and I would bet that "fair sport" in the past has encompassed a variety of personal risks by athletes and many approaches for maximizing athletic skill and achievement. One could certainly imagine ethical defenses of rules and practices that admit more risk than our current rules--reducing harm is an ethical basis for those rules, but need not be the only basis for constructing rules about sport.