To me, our triumphs will likely never out weigh our failures. There are a small group of people in this world doing amazing things. However what is the point if we can't survive as a species? As technology improves, one day making something to destroy the world(bomb, nano-machine, virus, etc...) will be as easy and accessible as buying a toaster and if we haven't evolved mentally by then, none of our technology will mean anything. The world right now could be a vastly better place if people only cared a tiny bit more, but we have been so bought off by convenience that I don't think we ever will.
I'm inclined to be optimistic. Nature has been experimenting with viruses and self-replicating machines for a while now, and has yet to come up with a design that cannot be countered. Bombs are capable of causing mass destruction, but we're still a long way off from having a doomsday device as cheap as a toaster.
I also suspect that, given a century or two, we'll have discovered ways of spreading the risk of catastrophic events. Perhaps by regularly downloading our consciousness and distributing backups across the solar system, perhaps even a few sent to neighbouring stars: "Alpha Centuri Backups - Just In Case Some Jackass Blows Up The Sun".
