This fallacy is also informally known as appeal to popularity. The argument usually goes as follows; Most of the world believes in X, therefore X must be true. This argument is fallacious in reasoning because popular opinion can be, and quite often it is, incorrect. The most popular and well circulated argumentum ad populum is the “every one’s doing it” argument. We all used this well worn argument when we were children and did not know how to reason properly.
Sometimes, this fallacy is used as evidence. In the past, it was thought that smoking must be a healthy pastime, since so many people participated in it.
