Prejudice:
Over 40 years ago, Martin Luther King asked us to judge others by the content of their characters.  Unfortunately we have yet to reach this ideal.  Study after study has shown that, even when we aren't aware of it, we judge others by their gender, race, appearance, and a host of other superficial qualities.  And this problem is not just a moral one, but an economic one too, because prejudice affects decisions about hiring and paying employees.  For example, a recent study found that identical job resumes were more effective if the name at the top sounded white than if it sounded black.  Prejudices are basically dangerous short-cuts: ways of judging people without really learning very much about them.

Typism:
I've noticed a disturbing tendency among some Enneagram enthusiasts to apply subtle prejudices based on personality.  "We need a 1 to do this job", or "I hate 9s", are some examples, but there are many others.  Many people are tempted to think that once you've got someone's "type", then you really understand them deeply.  Nothing could be farther from the truth - there is an incredible amount of human variation even among people who are supposedly the same personality "type".  In the business world, the Enneagram is not yet a widely used personality test, but it is probably making headway.  I'm all in favor of greater understanding of human psychology in the business world, but I am concerned that personality testing can easily be misused as yet another form of prejudice: yet another way of judging people without really understanding them.

As the Enneagram becomes more scientific, it is even more important to avoid the trap of prejudice.  For example, my own research on marriage patterns shows a lot of Enneagram-related effects: e.g. female 8s marry male 9s much more often than any other type.  Does this mean that all female 8s should marry 9s?  Does this mean that a female 8 who is not married to a 9 is headed for trouble?  Absolutely not.  There are many exceptions to even the strongest Enneagram correlations, presumably because there is a lot more to a good relationship than just personality.  People with the "right" personalities may not put any effort into their relationships, and people with the "wrong" personalities may be able to overcome some of the supposed disadvantages of that particular combination.

What to do?
I think it is useful to remember that personalities are just raw material - they are psychological tendencies and fixations that we can use or misuse in a myriad of different ways.  This raw material is relatively simple, while the finished product - a human life - is extremely complex, and not easily predicted from one's personality.

I think we should also remember that no one is a "pure" type, and that the Enneagram types are merely stereotypes - idealizations that in fact are rarely seen in the real world.  The best Enneagram teachers all recognize this.  However, part of the allure of the Enneagram is the idea that we have a "dominant" type - and that we can all be boiled down to a single number.  Although the best Enneagram teachers recognize this is wrong, it is very easy to forget this.  As soon as we forget this, we've turned the Enneagram into yet another system for stereotyping and prejudice.