The best argument in favour of anti-doping rules is that it's bad for athlete health.
We don't prohibit downhill skiers, auto racers, boxers, and competitors in god-knows-how-many high-risk sports from taking far greater gambles with life, limb and brain function. No one flinches when prizefighters get in the ring without head gear and punch each other into senility. No one frets over high wire and trapeze acrobatics. Why do MLB, NFL, NBA, Olympic, and Tour de France athletes over the age of majority merit special protection from the potentially harmful consequences of their choices?
I don't buy that concern for the athlete is beyond the doping prohibition at all. There are only two real concerns for those who make money staging and promoting spectator sports: (i) will allowing players to dope bring in fans or will it repel them; and (ii) will an exploitative Congress strip a league of its antitrust exemption in the name of shielding the purity of American youth from the siren call of doping sports stars.
I've always thought the Russian roulette scenes in The Deer Hunter
could serve well as a metaphor for professional sports.