True fans have to speak out for the good and against the bad in the sport. This is true of any sport or anything else with a following. When someone does something bad, given that it's the sport we love, we have an obligation to speak out for the best of the sport. It may create some short term pain for the sport but the long term benefit of holding the sport to a high standard is what matters most.
I understand that what she's talking about isn't necessarily what I'm bringing up but I think it follows a similar logic. First, who says people are denigrating Culpepper, Kastor, or Cox? Maybe they are just saying that London should be giving its appearance money to a runner who is closer to her prime, maybe they are just telling the truth about the field Culpepper competed against in order to keep perspective on her performance, maybe they are just saying that there are others who deserve more attention than Cox. Are these bad things to say or are they just the truth? If we shouldn't speak the truth, well, why speak at all?