I have three close friends (esfj, isfj and istj) - about 10 years of friendship with them - who are seem to have "type 6" characteristics and they are emotionally healthy and stable people.
Then there was that entp friend from high school who was a true phobic (she was generally emotionally unhealthy), and then suddenly turned very counterphobic and emotionally agressive at the age of 17.
The change from phobic to counterphobic was permanent and it essentially looked like she turned into an opposite of everything she was before.
I found her likeable as a phobic, but I couldn't stand her counterphobic side - in her friendships, it was like she would often disagree with people just for the sake of disagreeing, and was ready to verbally fight to death with anyone who would disagree with her about any little thing.
A lot of people seem to adopt a generalized opinion about "type 6" based on those phobic/counterphobic individuals, it seems.
EDIT: Lately I've spent some time researching the Enneagram theory, but I found out that the Enneagram theory has no real scientific basis and is not recognized in academic psychology, so I don't place any significance on it any more.