The truth of a proposition, however, is independent of the number of people who believe it. To argue otherwise is to commit the fallacy of argumentum ad populum (also called bandwagon, appeal to popularity, appeal to the masses, etc.).
When it does make sense to listen to people's 'opinion' is when it comes to those who are experts in a particular field, but this is because their beliefs are informed by the research and literature produced by expert professionals in the relevant field. Instead of being quacks driven by some half-baked woo-woo ideology, experts have the numbers and the evidence to back up their claims, and their beliefs are based on the evidence; they don't try to make the evidence conform to their beliefs.
Though the message in the following clip is directed to global warming deniers, the core message is one that can be equally applied to other groups of scientifically illiterate ignoramuses: creationists, flat-earthers, astrologers, homeopaths, or, and here is the delicious irony, anti-vaxxers... like Bill Maher himself :)
That's right, Bill. Vaccines are a medical issue; you're not a doctor, so you don't get a vote. Please shut the fuck up!
Of course, on the other side of the global warming debate, the evidence sometimes presented is not always what you'd call water-tight :)
Check out other entries on the environment.