I don't think he has done any real lasting damage, most people think cycling is/was dirty, yet millions turned out to watch the TDF in England irrespective of Armstrong and his doping...its done, gone, most people just don't care about Armstrong or the other dopers of the past..
BUT
I think within the next 10 - 15 years Armstrong will again be recognised as a great cyclist who won 7 TDF's, not officially, the fact he is an American will help alot and the character of the man, I just can't see him fading away into obscurity, even this film has change many peoples views on him..
Look at the "reverence" with which Tom Simpson is regarded
He was also a cheat and took illegal drugs to enhance his performance, yet this has somehow become an acceptable part of his "legend", and his death through the misuse of drugs somehow a heroic event