IP, you are at a point in your life, age wise and life experience wise, where you are being taught to think in a specific way. Specifically, because you are going for a doctorate you are trained to follow the basic tenents of the scientific method: facts, facts, facts. If it can't be empirically proven, it doesn't exist.
However, if you mature, about 15 or 20 years from now you will look back on yourself, and realize how little you know and how little books truly teach you.
There's a big difference between theory and experience. That's why people who work in detox centers are generally recovering addicts themselves.
HT has dealt with these issues both personally and professionally. Frankly, you are 23 and by your own admission have had a pretty good life. I don't think you need to correct him.
Has it occurred to you that maybe one of the reasons people find you irritating is because you're a little know it all princess? I'm not saying that as an insult, it's a fact. You were blessed to have a relatively sane childhood, your parents apparently are financially comfortable, you're cute ... frankly, what it comes down to is you're a kid with zero life experience who's basically talking out of her ass, okay? You don't know it all, you don't know half of it, and you could graduate cum laude and still not know it all, because you don't know it until you've gone through it and come out on the other side.
BTW, depressed people don't kill other people, half the time they don't have the energy to kill themselves. To do what that VA guy did, that fucker had RAGE inside of him and no hope left in his life.