I have to believe most or at least some athletes are clean to even watch the sport. If I were really convinced that everyone was doping and the athletes and federations were just putting up a "clean" front, I would be INSULTED to be watching. Not a worthy spectator sport at all. I stopped watching the Tour de France for a number of years and have only recently started paying attention again.
If they legalized PEDs (I personally don't want this to happen), that would be another story, because at least they'd be honest about what was going on. But how can you root for someone who is lying to you about their accomplishments? I would rather watch professional lawn bowls or "frolf" or my local freaking Turkey Trot where at least I thought it was an honest competition.