"Most of those (banned riders) who come back haven't suffered anything apart from a two-year salary loss, or less," the Garmin-Sharp rider told Reuters in a telephone interview.
"Everybody deserves a second chance but that second chance has to be earned. You can't come back as if nothing had happened."
Millar was banned for two years for doping in 2004, and since his comeback the Briton has been an active anti-doping campaigner.
Cycling is struggling with its credibility in the midst of the Lance Armstrong doping affair.
In August Armstrong was stripped of his record seven Tour De France titles and given a lifetime ban by the United States Anti-Doping Agency, which this month revealed the findings of its investigation into the American and his U.S. Postal Service Pro Cycling team.
USADA said it had provided undeniable proof that Armstrong was at the centre of a sophisticated doping programme. Armstrong has always denied using banned substances and never failed a test but decided not to fight USADA's charges.
Armstrong's team manager during his Tour de France wins, Johan Bruyneel, left his team, RadioShack Nissan, on Friday pending arbitration in the USADA case. Bruyneel is contesting the case.
Former dopers who shown no repentance are still in the sport, with Kazakhstan's 2012 Olympic road race champion Alexandre Vinokourov taking over as the new Astana team manager next season despite never apologising for blood doping in 2007.
Cycling's governing body, the International Cycling Union (UCI), implemented a new rule in July 2011 stating that doping offenders would be banned from working with pro teams, but the rule allows for leeway.
One of the conditions undermining it is that riders given a suspension of less than two years can still make their way back into the top teams.
Millar believes that admitting guilt should be part of the comeback process.
"The licence application should take this into account," the Scot said. "If there was somebody that (the UCI) think was not repentant, or has a negative effect on the sport, they could refuse it.
"There should be a rehabilitation process."
That would be under the guidance of the World Anti-Doping Agency, who could act "under recommendation of the UCI", according to Millar.
Yet Millar also suggested he would like to see changes in the governance of the sport, starting with the UCI.
"We need to change things from the top down," said Millar.
"I would like to help shape the future, we can really work together and find the solutions."
He added that coming to terms with mistakes is also a part of the rehabilitation process for guilty riders.
"We need to deal with the past, dealing with the past will help us shape the future," the 35-year-old said.
"We need to sit down with the teams, the riders, and even the fans, the media, all stakeholders," he said.
"We have to come to a common agreement on this, and that's when we can all move forward."
Armstrong has said previously there would be "no teary-eyed confession" from him.
Millar added: "(Armstrong) represents an era, he is the flag bearer of a generation. It's why it's coming down hard on him.
"The irony is that the sport has never been better. I mean the athletes have never been better but we still have the remnants of that culture, still have that refusal to deal with the past."