Pessimistic yes. People often tell me a lot of my own writing depresses them.

Suicidal, I doubt it. Outiside of very specific scenarios that target your life with surgical precision (like reading in the paper that XYZ corp's stock has collapsed to zero when all your wealth was in it), words are not really causal forces. They amplify existing tendencies rather than creating new ones. Even suicide cult leaders need personal magnetism to drive their followers to death. Writing alone will not suffice. I WISH words were that powerful. I'd perhaps make more money then.

If someone gets suicidal just by reading a book, chances are they were on the brink for other reasons anyway. Really good depressing stuff is so enlightening in other ways that you generally feel better after reading it (like Selfish Gene, Camus' Myth of Sisyphus or Catch 22). You feel like your eyes have been opened. You want to live if only to find out what else you've been deluded about.

For normal people, bad depressing stuff usually makes you question the writer's will to live or sanity, not your own. The Unabomber Manifesto is a good example (though it represents a murderous rather than suicidal mind). A friend made me read excerpts without telling me where they were from. Affter reading a few pages, a sense of "what's wrong with this guy?" began to grow on me.