The problem with allowing it is that there will always be that guy pushing the boundaries regardless of his health.
If you give every athlete in a certain sport access to a certain type of drug nobody will benefit from this drug. Thus they venture towards other drugs. First off, you are giving athletes from richer countries a benefit as they will be able to receive the newest and best drugs out there. Secondly, at one point there will be athletes crazy, desperate or brainwashed enough to do something really dangerous.
If you advocate just allowing certain types of enhancements then i see mostly the same issues. For example, American players could access better drugs then players from Argentina or Latvia. Doesnt seem fair to me at all.
I think what you mean is to allow players to take certain drugs to improve the overall level in sports. As you may already have noticed i renounce that. Only problem i have is that i am an avid cyclist fan who thinks that the Tour de France has become almost boring due to the dropping level of the cyclists (probably due to the absence of drugs). So yes, i am a hypocrite.
Also would you rather see del potro hitting a serve at 140mph or 170mph.
It depends. If it is wrecking his body then i dont want to watch that sport. We could also develop robots that play perfect tennis. Wouldnt that be even more exciting to watch? They are performing better hence it is more pleasant to watch?