I think Marma makes a good point about posters not knowing what to do with a clear psychotic episode (or given that this is online people lack clues to know what is a joke and what is a real situation), but I don't think most of the posts on that thread were full of grace and respect. The mentally unhealthy OP was mocked, even if it was not with ill intent.
If I was that poster and in a stretch of mental clarity I came back to read that thread, I would be pretty appalled with the responses to me while I was having a psychotic episode. It would be seriously depressing. I would feel terribly alone and dehumanized.
On the whole, I don't think the people who replied to that thread were intentionally cruel, and I agree that people were trying to deal with a situation they didn't know how to respond to. But does our motive for our behaviour matter? I think motive matters to some degree, but I also think that regardless of motive we ought to take responsibility for our actions.