"The real hopeless victims of mental illness are to be found among those who appear to be most normal. Many of them are normal because they are so well adjusted to our mode of existence, because their human voice has been silenced so early in their lives, that they do not even struggle or suffer or develop symptoms as the neurotic does. They are normal not in what may be called the absolute sense of the word; they are normal only in relation to a profoundly abnormal society. Their perfect adjustment to that abnormal society is a measure of their mental sickness. These millions of abnormally normal people, living without fuss in a society to which, if they were fully human beings, they ought not to be adjusted."
I find that a lot of highly socialized/extroverted people seem mentally ill - They tend to resort to common catch phrases to express themselves. They don't seem to have their own opinions about anything. They never seem to be able to justify the thought processes which led to their decisions or beliefs - Their line of thought about anything tends to be short and tends to link back to mainstream media rhetoric or religious dogma imposed on them by authority figures. They seem incapable of even basic self-analysis or introspection; they are only able to judge themselves and figure out what they want through the opinions and feedback of others. Also, they seem to lack creativity.
For me, this is pretty obvious because I know enough sane people that I can see the difference. Spending time with sane people feels great and is fulfilling. Spending time with normal 'highly socialized' people feels terrible. It's just very difficult to find sane people these days... Especially within certain social groups, many people are just incredibly fake and incapable of forming a genuine relationship.