Following the herd Argumentation type bac

First of all, what do we mean with the expression “to follow the herd”? The metaphor seems to refer to the animal world, and in particular to sheep. They are said to be rather stupid animals as they tend to mimic each other.
It then seems that the expression refers to people who mimic other people without paying attention to the reasons why they do it. However, why would it be wrong to do so?
On the one hand, we could argue that doing as people do is not necessarily a mistake. Indeed, one person could, for example, set an example in a particular field. This is typically what happens with athletes. Some of them are extremely well-known, they are everywhere on our screens, be it TVs or computers, and are considered by many teenagers as icons. As a consequence, many teenagers want to walk in their footsteps.
On the other hand, the idea of blindly following other people is, to some extent, scary. Indeed, fashion for example is not an example to follow as the model it provides to young girls is extremely thin models whose diet must not be followed. The same goes for social networks. It is not because most people surf the web and resort to social networks to communicate with their friends and family that one has to do so.
Following the herd with no proper reason to do so is obviously a mistake but when it comes to good initiatives, why wouldn't people follow a good example ?