"It is logically fallacious because the mere fact that a belief is widely held is not necessarily a guarantee that the belief is correct; if the belief of any individual can be wrong, then the belief held by multiple persons can also be wrong. If for instance, a logical proof that the answer is A attempted to make the argument that 75% of people polled think the answer is A, there is a 25% chance that the answer is not A. However small the percentage of those polled is distributed among any remaining answers, this chance by definition disproves any guarantee of the correctness of the majority. In addition, this would be true even if the answer given by those polled were unanimous, as the sample size may be insufficient, or some fact may be unknown to those polled that, if known, would result in a different distribution of answers." - from the wikipedia entry - my emphasis.
As Isiac Asimov said, "Every society prior to ours believed that the sun revolved around the earth... should we take a majority vote on it?"
I really like that logically saying that 95% of the planet believes in god is proof that there is a god is completely fallacious.
More to come on these lines, as i am reviewing logical fallacies to keep my wit sharp and also to try and prevent myself from using them.