A lot of people (mostly people who haven't dealt with it themselves) can be real loons (so to speak!) about depression. I agree with you that depression can kill you as fast or faster than many of the physical illnesses that people are so scared of. I have been a type I diabetic for most of my life, and suffered from serious depression even longer (at least since I was 8). For about six years I quit seeing endocrinologists for the diabetes, because I had had several very traumatic experiences with them (I won't get into that here), and I felt I could handle it myself for awhile. Anyway, all of my GPs freaked. They were constantly bugging me about going to see an endocrinologist, but no one EVER asked about my depression/OCD/panic attacks and seeing a psychiatrist. And my depression was so bad, it's a wonder I'm not dead. So I totally see your point.
I think people are such loons about depression because a.) they usually don't understand it if they've never had it, and b.) humans, as a species, have convinced themselves that they're special based on their brains. If you define yourself as a human based on your mental powers, then anything that affects your brain will be taboo. That's my theory, anyway. Along those same lines, prostate cancer may affect your life, but it doesn't usually change who you are as a person in any major way. (I realize all experiences affect us, but we're still basically the same people afterwards.) Any kind of mental illness usually does change who we are at a more fundamental level, though. So while I think it's stupid that it's so taboo, given that it affects so many people, and is just as physical as so-called physical illnesses, those are my theories as to why. Not that you asked...
I wish you luck and strength in your struggles with both the prostate cancer and the depression, and hope you get better soon.
29 yo female with two fuzzy children: a Pom named Snuggles and a Pom mix named PomPom.
Health History: Type I diabetes (19 years), allergies/asthma, hypothyroidism, osteopenia & multiple fractures, iron-deficiency anemia, Crohn's (of course), and depression (go figure.)
Crohn's History: May have had it since I was 11 (1988-89), definitely have had it since I was 15, was diagnosed when I was 25 (2003), was un-diagnosed in 2005 and re-diagnosed June 2007.