Evolutionary progress has an element of luck (sure we could be wiped out by a meteorite tomorrow) but negative events so far have been relatively rare.
IMO, you're reading your trend lines wrong - failing to properly account for the decrease in warfare and the rise of surveillance technology.
We are not talking about a "nontrivial chance" here. We are talking about "existential disaster seems likely". I read that as meaning the chances seem greater than 50%.
I find it very, very hard to estimate the actual chances of any particular existential disaster. I would not put that chance below 20% this century.
The sad news broke tonight : Neil Armstrong, the first human to ever walk another world, died today. We lost him forever. He died before we could defeat death.
Once again the horror of death strikes. This time, in addition from wiping from us forever a hero of humanity, he wiped from us forever a memory that will never exist again. Never again will a human being be able to experience being the first to walk another world. That beautiful experience is lost forever too, along with all the memories, dreams, desires and wishes that made Neil Armstrong.
But thanks to him, humanity made a giant leap. We'll fill the stars and conquer death. The spark of intelligence and sentience will not extinguish. That's the best we can do to honour him.
Source : http://www.reuters.com/article/2012/08/25/us-usa-neilarmstrong-idUSBRE87O0B020120825