[Lukas_Skywalker]

Raising the amount of red blood cells gives you an advantage because the blood can carry more oxygen. This leads to a race where everyone tries to raise it as far as possible. This is quite dangerous, because the blood gets ever thicker (which leads to thrombosis, as with the cyclist Tom Simpson in 1967). Banning blood doping helps to protect the athletes as well.

[cmiller1]

Pretty much all bans against PEDs and doping are to protect the athletes. If you allow them then the winner is whoever pushes their body furthest without going over the point that kills them, and a lot of people end up going over.