I certainly believe the Chinese performances should be considered suspect. Huge improvements, limited competition, and uncanny depth in some of the races lead most of us to believe there was something fishy going on. However, none of their record performances were ever invalidated due to a positive test.
So, it's hard to justify other top performers as unquestionably clean because they never tested positive. The good cheaters are typically miles ahead of the testers. I've asked this question before on this board: how many distance runners have ever tested positive for EPO? The tests have only been available for a little while. And again, EPO is already an old drug as the cheaters have moved on to bigger and better things that can't be tested for yet.
All we can say about a top performer who hasn't tested positive is the following: they are neither clean nor dirty; they haven't tested positive.
Don't take this the wrong way. I have enjoyed watching the outstanding performers over the past 20 years - Paula, Geb, Michael Johnson, Flo-Jo, Tergat, etc. No matter what, they did the training and achieved the performances. We just don't know if they had illegal help or not. So when I see a WR or other phenomenal performance, I enjoy it and then place an "*" next to it in my head. The "*" means I don't know.
As for the racial aspects of the topic, there is certainly something to that, although it's deeper than that. People tend to believe the performers who are like them, or those who are who are from the same country, or those who project positive values & work ethic.
The Chinese were very different (and again, downright bizarre performances went along with them) and therefore very suspect - although they never tested positive. But white athletes such as Mary Slaney, Uta Pippig, and Dieter Baumann all tested positive and had a large following of supporters.
Ben Johnson (who did test positive) was different and unlikeable (he was Canadian/Jamaican, stuttered his way through English and swore at US hero Carl Lewis) and therefore was unbelievable. But Americans like Flo-Jo, Marion Jones, and Michael Johnson (all being US citizens who never tested positive) are/were considered clean by the masses - even though they were all phenomenal performers with questions floating around them:
Flo-Jo's 1988 performances were/are untouchable, but the masses don't question her performances, even though she retired immediately and later died at a young age.
Michael Johnson's performances (esp 200, but even 400) were/are untouchable, and he didn't seem to ever field many drug questions.
Marion has dominated the world sprint scene pretty much since her return to the track. Even though she's a dominant, very muscular sprinter with a positive testing shot putting ex-husband, most people seem to consider her clean.
Paula Radcliffe's 2002 season was one of the best ever, even considering it was a non-major year. Her range was incredible (3K to marathon). And to most people, she's very likeable - she displays a positive attitude, strong work ethic, and complains about doping. Also, she's white and English. Again, I don't think of Paula as clean or dirty - she hasn't tested positive. But if I was a top performer who did cheat, I would take the same public stance against doping as she does. Because if she does test positive, she'll be suspended anyway - which is worse than being considered a hypocrite. Plus, she can say that as a strong doping opponent she makes a great target for tampering or sabotage (as Dieter says).
So, in the meantime, I enjoy the performances and place my "*" next to the great ones.