"This kind of behavior is more of symptom than a disease. There is no defining line for when something crosses over into "disease"."

Well, actually there kind of is. It's different for each disorder, but there are pretty specific criteria for each. Many behaviors that are included in a psychiatric diagnosis are indeed, normal, i.e. sadness, but they become a disorder when they are taken to a pathological extent. A key criterion in most psychiatric disorders is that it "interferes with major life activities". So being sad is not a disorder. Being very sad, plus having at least 7 other symptoms, for more than two weeks, without any physical or substance related cause, and not better accounted for as grief or bereavement, and interfereing with work or school, that is clinical depression. Washing your hands? Normal. Washing your hands over 100 times a day and experiencing extreme anxiety when not able to wash your hands for any length of time? OCD.

Being diagnosed as having a mental illness should be the first step to getting treatment and overcoming the problem. That people (patients and their families and friends) resist the diagnosis is because of the negative connotation, stereotype, and discrimination people such as yourself apply to what should be as neutral a label as being told you have a physical illness. And to the comment about people who are eccentric and just fine to be so? Some of those people might fit some of the criteria of a mild disorder, but the fact that they're not bothered by it, in most cases means they wouldn't be diagnosed with one, since most (not all) disorders require that the individual be experiencing distress. And again, (unless they're not threatening themselves or others), they need not recieve treatment. People talk about psychiatric treatment being 'forced' upon them. While that does happed, more often the scenario is someone who wants and needs treatment and can't get it (usually because of cost).