I think both sides are projecting their own view a little too hard on this.
Environmental factors surely are a factor in this and I was 'quoting numbers' because VladRussian was a little to quick to dismiss mental illness. Again - since we all don't know the details in this particular case, this is an abstract discussion about suicide. In an abstract discussion, you either make a case and discuss it, or you discuss one that another person has made. VladRussian simply picked a fight and Cushman bought into it.
Also, re: circular logic. I don't think it is circular - Suicidal thoughts may be a symptom of depression, but that's not the same as saying they are a cause of depression. I know you don't say that either, but that's what would make it circular. (Also: saying it's 'somewhat circular' is a cop-out - it either is, or isn't circular.) I further don't think mental disorders really are "blamed" for suicide, they are simply accepted as a very common pathway in medical studies.