I've suffered some cases of extreme, acute depression in my life, and I was lucky that I had some support that prevented my depression from killing me.
That said, I'm really uncomfortable with the language that somebody else can be, as you put it, "responsible" for someone's suicide. One of the things that is really driven home in therapy for depression (that is, after you're no longer in a suicidal state) is that you alone are responsible for your actions; you're not merely at the whim of your circumstances.
The harassment from Kiwifarms is/was reprehensible, but harassment alone, at that level, is enough to draw a social and legal response without pretending they are responsible for someone else's suicide.