Ill tell you whats going on....
It is an "open secret" among sporting professionals all over the world that the only thing that matters about doping is WHETHER OR NOT YOU GET CAUGHT. IF YOU DO NOT GET CAUGHT, YOU DIDNT BREAK ANY RULES.
Thus, Lance Armstrong is pissed off that people have been calling him a cheat, despite not being CAUGHT. He knows that this contravenes the 'etiquette' of sport and feels like he is being picked on (which may be the case).
However, the point is that he has been doping. Obviously. He was just pissed at the amount of "undue" attention he got over it. MANY MANY sporting "greats" use performance enhancing drugs. It is as simple as that. Part of the "sport" of "sport" now, part of the "science" of "sport science", part of the challenge in "international challenges" is AVOIDING BEING CAUGHT DOPING. Its all just part of the game (sport?).
In a few years time this is going to be blown wiiiiiide open, some sports will allow "drugs" and others will not. Eventually, all sports will be forced to allow "drugs" because there is no way, NO WAY to prevent all participants from doping in some way. I am not exaggerating. The public has no real idea about this, sporting associations keep it under wraps, but everyone, EVERYONE whos job is sport knows that around 60% or so of pro athletes are on performance enhancing drugs.
Just another evil come as part of mankind's progression.