"In my mind, I think cycling is one of the cleanest sports because it catches the cheats and throws them away," he told Sky Sports News.
"The same question I always get is, 'how can cycling move forward?' Well, it is moving forward and it has been - but people won't let it.
"There are going to be cynics, there are going to be people with closed minds, and there's going to be stuff that comes up from the past.
"That's not fair to tarnish the riders who are doing it now with the brush they don't deserve to be tarnished with. It's a stupid, closed-minded view on it.
"Cheating happens everywhere - in every sport, in every country, in every aspect of life."
How does blood doping work?
Millar, who served a two-year ban after admitting to doping in 2004, is now a member of the athletes committee of the World Anti-Doping Agency.
Usada's report states that the era in which Armstrong dominated was "the dirtiest ever" and Millar believe it was clear to everyone in the sport that drug-taking was prevalent among many of the top cyclists.
"The UCI have to accept they have to carry some responsibility for this because it was obvious what was going on," he added.
"The UCI had all the blood data, the medical reports, it was part of the culture of the sport and in the big races the majority of riders were doing it on drugs.
"There was only a tiny minority getting good results without drugs and they really were the outsiders."
BBC Radio 5 live Sport will look at the Lance Armstrong saga in a special programme on Monday at 19:00 BST. 'Peddlers: Cycling's Dirty Truth' includes interviews with Armstrong's former team-mate Tyler Hamilton, former Wada head Dick Pound, and British cyclist David Millar, who was banned for two years after admitting taking performance-enhancing drugs.
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