Good comments, including a couple of corrections of my errors: Lance Armstrong won seven straight Tours, not six, and I meant to write Barry Bonds, not his excellent ball-playing father Bobby.
Perhaps Armstrong used drugs and Landis did not, but I believe it was probably the opposite. However, I admit that neither claim is proved beyond a shadow of a doubt.
If exercise, diet, etc helps an athlete do better in baseball, football, cycling, and other sports, in the absence of regulation, participants would do these in amounts that exceed the optimal levels in their attempt to do better than others. In particular, they might exercise to the point that actually lowers their long run-health. If athletes in contests could control the amount of exercise that everyone takes, they would want to do so. Clearly, however, enforcement would be impossible, so they do not try to implement any controls.
My support of restrictions on the use of various drugs in organized support is not inconsistent with my support of legalizing drugs. I believe people should be free as individuals to use steroids and other drugs, but that is not the same as believing that major league baseball, or the Tour de France, should not have the right to limit the amounts of certain drugs or other chemicals used by participants. No one is forced to enter these races and contests. If bicycle fans want bicyclists to use drugs in races, those races that allowed them would prosper relative to those that did not. To be sure, this argument is less persuasive for major league baseball since they face little competition from other leagues, although baseball does face competition from other sports.
I am not advocating paternalism. "Paternalism" prevents certain behavior that people would engage in if they were not constrained by laws and regulations. Most athletes would support outlawing doping if that could be effectively enforced.
The analogy of drugs in sports to illegal immigrants is not apt. If employers were punished for using illegal workers, that cost has to be added to the cheaper wage of immigrants. If neither the immigrant nor employer had to fear punishment, there would be no competitive advantage from using illegal workers.