Depression is dangerous.
Why? Well, there are a multitude of OBVIOUS reasons. But, coming from one who has been there, the worst part is that you don't care. When you're depressed, people may or may not try to be friendly, helpful, and the such to you. Regardless of that you feel alone. And when people try to insert themselves in your life, you tend to extract yourself from theirs. In essence you typically perpetuate your own depression until somebody tackles you and doesn't let you go until you feel better, you just suddenly decide to hell with it and go running through a public place naked in the middle of the day (Yeah, that'd be me), or you either succesfully or unsuccesfully kill yourself.
And that, I'd have to say, is what makes it so dangerous. Fact of the matter is, very few people look for other people who are depressed and recognize is. And, said depressed people don't really seek anybody out.
Nofeeblechrist has an opinion on the trivialization of depression, if you're interested. I decided I'd jump into why it's so fucking dangerous. After all, Suicide is still a leading cause of death. Maybe not THE leading cause of death...but it's up there.
Living of course, is the leading cause of death.