Birdsong said he was attracted to the organization after his wife -- an avid cyclist -- was diagnosed with breast cancer in 1998, about when Armstrong won his first Tour de France title.
In 2007, the couple "became part of the public face of the foundation," said Birdsong, a software engineer. "I was one of the people who would answer questions from people to raise money."
Though he had long been aware of the murmurings alleging drug use by Armstrong, he said he didn't believe them. "I was a huge Armstrong fan from 1999 to the time he retired; I would defend him from anyone."
But, as his involvement with Livestrong grew, "I started to ask what are they doing with all this money they are raising?"
The foundation's IRS filing last year reported more than $100 million in net assets or fund balances.
The organization spent $2.1 million in compensation to its seven highest-paid officers and three employees, according to the IRS form. No member of the board -- whose members include CNN Chief Medical Correspondent Dr. Sanjay Gupta -- was compensated, it said.
Now, Birdsong said, he feels disillusioned. "The whole thing is founded on a lie. The guy cheated and he forced other people to cheat. I would like my money back. We donated under false pretenses."
A Livestrong spokeswoman did not return a call and e-mail seeking reaction.
Bob Kile, of Kent, Washington, said he is unfazed by Armstrong's resignation from the foundation's top job. The 65-year-old throat cancer survivor he has no plans to remove the yellow bracelet that identifies him as a donor to the foundation.
"If Lance doped, that certainly takes away from his athletic wins," Kile said. "However, to survive what he did and come back at all is impressive. To come back and create good like he did with Livestrong is even better."
Actor Sean Penn expressed a similar view on Friday night, as he entered the Austin Convention Center for the anniversary event.
"Of course he remains an inspiration," Penn said in response to a reporter's question. "I think anybody who's looking with a very clear eye at this would find themselves very hypocritical to consider otherwise."
The editor-in-chief of Bicycling magazine, Peter Flax, told HLNTV.com that he thinks the scandal would have an impact in the short term -- but that people should understand that cycling has already made moves to clean up its act.
"The next year or two will be difficult and pivotal years for the sport. People need to understand that the sport is way cleaner than it used to be -- far cleaner and more transparent than most other elite sports," he said.