Correction -- all of the atheists you know who vocally express their beliefs have Star-Trek-like beliefs, or other generally optimistic beliefs about the future

Correction -- all of the atheists you know who vocally express their beliefs have Star-Trek-like beliefs, or other generally optimistic beliefs about the future. The atheists who think that there's a significant chance that we'll manage to wipe ourselves out in the next century generally aren't going to vocalize those beliefs, unless there's something actionable that can be done about it (though I don't think I actually know anyone who thinks that ecological overshoot is a real threat to civilization, much less humanity). I think you see the pessimists on both sides of the secular / religious divide. The difference is that pessimism is generally low-status and frowned upon in secular groups, meaning that pessimists in those groups are generally not very vocal about their pessimism.