This fallacy is also called "Argumentum ad Populum". This is when someone tries to make their argument based on the fact that it is a popular choice among people, or what most people believe. It is an extension of the Faulty Appeal to Authority. If it is wrong to appeal to one person who is not a legitimate authority on a subject, then it is just as wrong to appeal to multiple people who are also not experts on the subject. 

Politicians frequently seek out opinion polls to determine which way they should stand on a particular topic in order to maintain their position in the next election. Self-preservation is not the best foundation on which to base important decisions. Using this fallacy to try to win a debate is also not a good foundation for sound outcomes. 

People, as a group, seldom make good decisions anyway. While a small group of individuals may exhibit rationality, larger groups are susceptible to manipulation. We refer to this psychological phenomenon as "mob mentality" or "diminished responsibility." When others get away with something, people become less inhibited and emboldened, as well as releasing some of their general tension, excitement, frustration, or anger safely unseen within the herd. 

If an individual truly lacks a preference or lacks knowledge about a particular topic, they may simply adopt a passive approach and go with the crowd's choice. This has an accumulative effect as the number grows. As the number grows, the degree of error may also grow. Popularity seldom produces a sound, rational, well-balanced outcomes.