I came across a webpage which makes this claim."Skeptics of homeopathy insist
You are probably thinking of the informal fallacy, Argument ad Populum or Appeal to the Masses, in which someone suggests a conclusion is true because many people believe it to be true. http://en.wikipedia.org/wiki/Argumentum_ad_populum
While large-scale belief might provide inductive evidence for some claims, we know the masses can be wrong about lots of things, especially in cases where the underlying explanations are complex, as in medicine. That most people believed the sun goes around the earth did not show that claim is true. That most people did not (do not?) believe tiny things (germs) cause disease does not show that belief is true. That many people think homeopathy works provides little or no support for that claim.
However, there's an interesting twist in this case: the placebo effect is remarkably powerful--if people believe some medical treatment works, that belief can have effects, especially when it comes to pain. So, many people believing homeopathic treatments work might have some causal effects on whether it works, at least for those people. But I am dubious that the placebo effect can cure cancer or kill viruses...