The reason I feel comfortable stating this is simple. Insanity is, ultimately, a (non-quantitative) measure of normalcy based around how well a person is able to interact with other people around them. It can have a variety of causes, ranging from the individual's genetic heritage to chemical imbalances derived from their environment, to how they understand and behave toward their own personal history. Psychopathologists and abnormal psychologists have developed a variety of approaches to studying, explaining, and treating such problems, appropriate to the individual problems as they are discovered and recognized, but because of the diversity of the field and the nature of the problem it's difficult to speak of as a whole. How do you distinguish someone with actual mental problems from someone who's just rather strange?
To address this issue, four basic questions are used to determine whether a person is insane:
- Deviance: Are the person's thoughts, emotions, or behavior typical of their culture? (Note the specificity of 'their' culture. This is not used to condemn an entire culture or subculture that deviates from the rest of society; it's been a huge problem historically, as I'm sure you can imagine.)
- Distress: Is the person troubled or deeply emotionally affected by the way they think and act? Do they feel in control of themselves?
- Dysfunction: Is the person impaired in their ability to survive? Can they get by in life on a day-to-day basis?
- Danger: Is the person prone to violent or injurious behavior, to themselves or to others?
So, if you're one of those people, congratulations. You're adapted to society. You're normal enough to get by. You're not less special. You're better off.
Okay. Now flip the coin over and stare at the other side.
If insanity doesn't mean a lot of things you thought it did, the same is true of sanity. Sanity doesn't mean you know what you're doing. Sanity doesn't mean your beliefs and thought processes are true to reality. Sanity doesn't mean you're rational. Sanity doesn't mean you understand. Sanity means you're adapted to society and you're normal enough to get by.
Society is a vast and amorphous beast, a picture puzzle where the pieces are constantly moving and being joined to other pieces and all kinds of different pictures can be created from largely the same pieces... a piece that is considered insane in one particular subset of society may be perfectly well-adjusted to another. And then we could consider phenomena like hallucinations in the sane which 10% of healthy, sane individuals will experience at least once in their lifetimes, despite being almost universally associate with insanity in the popular mindset.
But more importantly than any of that, as far as I'm concerned, is the sticky ethical morass of whether being well-adjusted to human society is in itself a good thing. There is a long, long list of psychological observations demonstrating that human beings do not think clearly or reasonably, do not understand the world around them, do not understand each other, and even do not understand themselves... when you think you have a pretty good understanding of it all, and so does everyone else. It's called cognitive bias.