[corin_]

To add to your answer: mental illness isn't all or nothing, it's not either you're a normal person with free will vs. you're crazy and everything you say is crazy. People with depression, bipolar, many other mental illnesses could be completely normal when you meet them but still classified as having a mental illness. It's possible to keep a normal life, a normal job, yet be aware that you are, in some way, "mentally ill".

[cryoshon]

This is exactly the problem! The label of "mental illness" is enough for people to throw out the complete capacity of a person merely because they have troubles in a few spots. It's frustrating.

[marrs]

Add people who don't sleep enough, are pregnant, are facing redundancy, are approaching middle age, have an addiction, etc, ad infinitum.