There has been doping in professional cycling since the early days, with riders taking amphetamines and champagne (the light bubbles makes for fearless descending), among other things. It is profoundly part of the culture. EPO is relatively accessible to Cat 1-2 racers on the regional scene, who really thinks it wouldn't be for pros?
Doping is the only way to remain in the peloton, meter of elevation after meter of elevation, kilometer of suffering after kilometer of suffering, day after day, week after week. This is a BRUTAL sport (compared to, say, triathlon, where pros do not race more than every week or every other week). This doesn't mean that these guys are not exceptional athletes. But when a drug like EPO can improve one's capabilities by 10-20%, well that's over 6 minutes per hour.
I'm not mad at the racers as I feel really sorry for them. They have to close their eyes to whatever is going on, they ingest all sorts of things with or without knowing (or rather without wanting to know), they put their health at tremendous risks. The team directors and soigneurs are very well aware of what is going on. But it's these guys' dream to be in races like the Tour de France. Not doping, or speaking up about it, will mean the end of their dream (and lawsuits, and losing whatever respect they had received from racing, and conflicts with their friends and families, etc.). Sure, they have a choice: doping or quitting pro cycling. And they have to keep lying all the time, to others but also to themselves, to their closest friends and family. That must be awful.
Now that controls are stricter, things get messier, I'm afraid, new stuff is tried out (blood transfusions), drugs are taken as a cocktail (sub-detectable doses of individual drugs which together make a powerful mix, with possibly lethal effects), sometimes the guesses are wrong, or the dosage is not quite right, and they get caught. Other times, as has been seen in a number of occasions over the history of cycling, they die.
There might be an oddball here or there that's not taking anything at all, and that has never ever touched anything (knowingly at least), but that would be really rare I'm afraid.
I am not sure it was meant like that, but I increasingly see the Triplettes de Belleville as a metaphor on the doping. They race the cyclists until they die, who cares about their physical and mental health?

