What are some examples of the ad populum fallacy and how does it impact the validity of an argument?

The ad populum fallacy occurs when an argument is based on the belief that something is true because many people believe it. Examples include "Everyone is doing it, so it must be right" or "If it's popular, it must be good." This fallacy can impact the validity of an argument by relying on popularity rather than evidence or logic to support a claim, leading to a weak or flawed argument.