Oo and my thoughts on everything:
I think the diathesis stress model is most logical. However, what makes me rethink this and say it's all biological and "triggers" don't cause full blown psychological disorders, is because of psychopharmacology. If someone takes prozac, and it works like it usually does, then the individual will not become depressed, even in an environment that is unhealthy. With the right combo of drugs, a person can be happy and energetic, depressed and anxious, or calm and careless, regardless of the situation they're in. Does this not disprove environment being considered a factor?
I disagree. Diathesis-stress model says you need both biological predisposition and environmental factors for a disorder to occur. Take away the biological "predisposition," and the disorder should disappear. At any rate, I think one of the better disorders to look at environmental effect would be borderline.
Regarding DID, I don't think people have multiple personalities in the sense that one of their "identities" is a middle aged man and the other is a teenage boy. I think that people use this "disorder" as an excuse. For example, they can say "oo one of my personalities is Bob, he's a mean and aggressive person who loses her temper easily." By doing this whenever they get in a fight with someone or react in a way that embarrasses them, they can free themselves of blame and say it was out of their control because they have this disorder. A defense mechanism because they don't have to blame themselves anymore. Also maybe a way for them to get attention...
Being a defense mechanism doesn't mean it couldn't be unconscious and uncontrolled. E.g. dissociative amnesia.
I don't think people are being diagnosed with mental disorders too much. Critics say that the estimates of people with depression and GAD and personality disorders are too high and that they may even trivialize psychiatric diagnoses. They say that characterizing someone as mentally ill doesn't mean much if the label is applicable to half of the population. Well I say why not? No one in this world is completely healthy. A cold here, an ear infection there, people could always be healthier physiologically. I compare a cold physiologically, to mild anxiety psychologically. With a cold you rest and drink lots of fluids, but you're not on any drugs usually. With mild anxiety, maybe youre in group therapy and learning relaxation techniques. However, many people have cancer and diabetes and high blood pressure. Many people also are unhealthy mentally. No one says cancer is over diagnosed. Why should bipolar disorder or depression be?
The DSM outlines guidelines for diagnosing disorders. I don't think it's particularly useful to redefine what a disorder is for this question. In the context of DSM guidelines, my answer would be "some are overdiagnosed, some are underdiagnosed" with more emphasis on the underdiagnosed.
Determining sane or insane. A bipolar person is not delusional. They understand reality, they just can't control their emotions. Even if they were incredibly angry and sad, they knew they were killing a person, so they should be punished.
This article outlines some interesting stuff. The laws vary from state to state, but this outlines Maryland. I'm curious what constitutes volition impairment, as it seems substantially more subjective than cognitive impairment. At any rate, they seem to sometimes include manic episodes under VI.
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2710106/