"If there is no god, is there hope for mankind"
Definitely. If you look at the statistics, for example: Average human life expectancy, average available calories per day per human, infectious disease statistics and even population growth you'll notice that things overall are getting better over time for the entire planet.
Regarding climate change: The fact that it has been detected and debated is a very good thing. You can't fix something if you don't know its broken.
"Why do humans seem to be so unable to rule themselves."
Slowly but surely the world is democratizing. This is a good thing as it also goes hand in hand with free markets which is also a good thing.
Human kind can still drop the ball in a big way, but I think that we're on the right track.
Believing in God and the Watchtower does seem to give one comfort in that one supposedly knows the future, but this is an illusion. The future is an unknown country which makes it scary but also exhilarating at the same time.