That statistic presents a somewhat circular logic, with drug abuse (mainly alcohol) and mood disorders (depression: uni-/bi-polar) making up the bulk of the 'mental disorders' figure (FTA). Since feelings of worthlessness and suicidal thoughts are used to diagnose depressive disorders in the first place and since drug abuse is acknowledged to often be a form of self-medication for undiagnosed depression, blaming 'mental disorders' clearly begs the question in a large number of cases.
The literature shows that environmental factors play a major role in causing and aggravating these illnesses and behaviours. I believe this is the point that VladRussian was making and it's not so easily dismissed with 'numbers'. Likewise, the very large proportion of suicides which come after a clinical diagnosis (and presumably some kind of treatment) doesn't inspire much faith in the 'just go and get yourself sorted out' line of advice.
I find it disturbing that in a discussion on this topic, someone advocating being kinder to people in general, and perhaps certain people in particular, would be subjected to the kind of insults that Cushman has used.