What is performance-enhancement?
A brief ethical thought experiment:
Suppose we could measure something like heart health/performance (substitute this with another physical attribute of your choice, say VO2max, which is an indicator of aerobic endurance and measures the maximum amount of oxygen that an individual can use during intense exercise). One does not have a healthy heart or an unhealthy heart; as with all things, health lies on a spectrum, so let's put in some arbitrary numbers and ranges, with 100/100 being the Platonic perfect heart.
Suppose the healthy range for normal people 80-100, while the majority of elite athletes score in the 95-100 range (we should expect the health demands for performing as an elite athlete to be higher), and a drug exists to improve your heart score by 5. In a way, the drug is designed to get the 75s up to the normal healthy range.
Certainly if someone is at 100, and they take the drug, they would now be superhuman, and such performance-enhancing is outright wrong.
But would it be wrong for an athlete scoring 89-90 to get her score up to a 94-95, so that she is at or near a baseline level with other elite athletes?
What about an athlete who is already elite at 95, who wants to jump to a 100, and lead the pack while still having a health state that is naturally occurring in the population?
In other words, do we have a notion of "healthy enough for everyday living" and "healthy enough to be an elite athlete"? When can we treat one kind of health issue and not the other? Should we let the genetic chips land where they fall, and accept that some people simply do not have the physical makings of an athlete regardless of their sport-specific skill, and if so should all supplements be disallowed?
Which notion of fairness do we prefer? There was a movie that touches peripherally on this; it was called Gattaca.
A single flow'r he sent me, since we met./All tenderly his messenger he chose;
Deep-hearted, pure, with scented dew still wet - One perfect rose.
I knew the language of the floweret;/'My fragile leaves,' it said, 'his heart enclose.'
Love long has taken for his amulet/One perfect rose.
Why is it no one ever sent me yet/One perfect limousine, do you suppose?
Ah no, it's always just my luck to get/One perfect rose.