“Everybody is doing it.”
This argumentum ad populum asserts that, since the majority of people believes an argument or chooses a particular course of action, the argument must be true, or the course of action must be followed, or the decision must be the best choice. For instance, “85% of consumers purchase IBM computers rather than Macintosh; all those people can’t be wrong. IBM must make the best computers.” Popular acceptance of any argument does not prove it to be valid, nor does popular use of any product necessarily prove it is the best one. After all, 85% of people may once have thought planet earth was flat, but that majority’s belief didn’t mean the earth really was flat when they believed it! Keep this in mind, and remember that everybody should avoid this type of logical fallacy.