1. a man of distinguished courage or ability, admired for his brave deeds and noble qualities
2. a person who, in the opinion of others, has heroic qualities or has performed a heroic act and is regarded as a model or ideal
Under that definition, Lance Armstrong was a hero.
People considered him a hero because he overcame cancer to win one of the toughest sports events in the world and—without being aware of his doping—that is perfectly understandable. He was more than just a sports person - he was a celebrity, an idol. It's no different to people looking up to football players, musicians or pre-eminent scientists. The point is he competed against the very best and overcame great adversity to become the top of his field.
Of course, now that he has been exposed as a cheat and a charlatan he is a disgrace to the sport and deserves condemnation, especially the way he continues to lie and exploit his admission for his own personal gain.
I like my musicians on drugs.
Problem with heroes, though, is hero worship. A bit of that going on right in this very thread.