Stereotypes about the Enneagram types come about when only a narrow set of characteristics are taken as a representative generalization. This can easily happen to someone new to the system.  Here are some example type stereotypes:

• All type ones are good boys or good girls
• All type twos are helpful
• All type threes are deceitful
• All type fours are depressed
• All type fives are feelingless
• All type sixes are fearful
• All type sevens are happy
• All type eights are pushy
• All type nines are pushovers

The Enneagram system is deceptively complex. Upon first glance it's simply nine different categories of personality type. The truth is that no matter how much time you spend trying to understand the system, there's always something new to learn about each type and the many variations. 

So, where do these stereotypes come from?

I think people are in search of simple descriptors or labels. When authors label types with these simple labels, they in effect promote stereotyping. Just think about it in terms of this definition of the word stereotype.

A too-simple and therefore distorted image of a group

What do you do about these stereotypes then?

As someone learning the Enneagram type system, just realize that the labels and simple descriptors give an incomplete picture. The labels and descriptors may not apply to every individual all the time - they may only apply to some individuals some of the time. 

What do authors and teachers do about using simple labels?

Some authors just don't use labels. Some authors use mutliple labels to represent both the positive and negative characteristics of a type. Some authors don't use a single word, instead they use a more meaningful phrase. Let's face it, readers want simple. If an author wants to sell their book then they have to give the readers what they want.

My solution would be to understand the types at the core level and create descriptors that contrast the differences between the types. I've found for that to happen, because the current system is insufficient, a new system would have to be developed that goes beyond the limitations of the current system. I'm working on that, but in the meantime, exploring these stereotypes should offer a more accurate understanding of the Enneagram types.