Popularity does not confer validity.
By that I mean that just because a belief is shared among a large number of people it is not automatically true, correct or acceptable. My aphorism is an almost poetic summery of the Appeal to Popularity logical fallacy.
The basic idea is that a claim is accepted as being true simply because most people are favorably inclined towards the claim. More formally, the fact that most people have favorable emotions associated with the claim is substituted in place of actual evidence for the claim. A person falls prey to this fallacy if he accepts a claim as being true simply because most other people approve of the claim. (Source)Many religious people contend that their beliefs must be true based on the millions of people around the world who share them. Naturally they don't allow that same argument to apply in the case of other religions that also enjoy a large number of followers. It's like saying that back when the majority of people in the West thought the Earth was flat it must have been truly flat.
Similarly, there are politicians who will attempt to convince us their policies are sound based on the number of favorable poll ratings they receive. "My plan to sell Detroit to the French must be a good move. 65% of the people in Kansas approve."
An appeal to popularity is an attempt to convince us something is true simply because a majority of others think it is. It fails to take into account the possibilities of misinformation or plain ignorance. It could only confer validity if no effort was made to find a better explanation for an observance. Had humanity arrested its exploration of astronomy in 100 B.C.E. we'd still think the Sun orbited the Earth. If medical research had stopped in the Middle Ages we might still believe illness was caused by demons or humors. Just because a lot of people agree on any particular belief does not mean that belief is sensible, logical or true.
Popularity does not confer validity.