Most people have no idea what mental illness is like, and how many people suffer (literally) from it, and how many people have it.
And I'm talking about this being separate from substance abuse, although substance abuse can allow mental illness to manifest itself, and those with mental illness are in danger of substance abuse because of the attempt to self-medicate the symptoms with drugs and alcohol.
Since the VA doesn't make people have insurance to be treated (as long as they are eligible veterans), we see a lot of MH/SA cases. I do think our population has a higher rate of these issues than does the general population, because of the military and combat experience, but I also think that it is way undertreated in the private sector due to the abysmal state of health insurance for mental and emotional issues. Most people out there suffer in silence, or appear on the 6 pm news for one thing and another.