Extraordinary claims require extraordinary evidence though, and barring said evidence, the simplest solution still tends to be more likely.
I mean, which is more likely to be possible?
A ten-plus year coverup effort assisted by who knows how many people, being able to fool labs in how many different places at how many different times, your life being put under the microscope for years on end
Lance Armstrong is a very talented, able cyclist.
I read a story about the 1992 USA Olympic basketball Dream Team, and one bit I remember was none of them wanted to be the top scorer for a game, because that meant a mandatory drug test (they hated the inconvenience). The more you win, the tighter the scrutiny becomes, and to keep it up for so long in Armstrong's case, I cannot imagine it *not* being leaked earlier (considering it appears practically anyone who's ever been a part of USA cycling was in on it...they're *all* that altruistic?) and to bring it up now reeks of being a witch hunt and farming for publicity.
But everyone seems to accept the conspiracy, so why not?