It's important to keep in mind that the argument is full of ambiguity.
-Forbidding doping is in sports is considered socially necessary, because it is believed that if athletes get to take potentially dangerous drugs then it's ok for anybody to take them.
-However, the athletes are required to subvert the rules in order to be competitiive and stay at the top of the sport. Hence one of the prices they pay to be a pro athlete is adopting a double standard--privately they believe themselves above mere morality and are prepared to do what they need to do to maintain or upgrade their sporting status. Publicly, they must condemn drugs and drug usage.
-Hence the temptation to legalize. But this runs into numerous problems, among them 1) social problems if ordinary people come to think of PEDs as ok 2) the problem of excess...if everything is allowed the extremes get more extreme 3) if the sport is percieved as drug-soaked fans lose interest.
-In the past, the science of doping has far surpassed the science of testing, and this continues today.
-It's also important to note that the leadership and mentors in the sport of cycling were participants in the doping culture at the time...indeed doping in cycling has a long history and goes back to the roots of the sport. But naturally it is essential for the sport to keep this buried in order to remain economically viable.
It's a structural problem. There are no good guys and bad guys. Just imperfect human beings in an imperfect system.