We can do both.
Lives saved versus dollars spent is a better metric. Having said that, the Singularity crowd tends to lump in all potential future lives into the saved category. The question of allocating resources to avoid existential threats very quickly turns into a Pascal's mugging in favor of AI safety (think of the trillions of future children).
> The threat of nuclear war is well known ... until very recently the same could not be said for the threat of unfriendly AI.
Enough nuclear weapons exist to kill all humans forever. Strong AI does not exist. Expert estimates range from decades to over a century. At the same time, the people making the most noise seem come from the side of avoiding existential threats and not AI research. I am (highly) skeptical they will produce anything of value. Let me rephrase. Would you expect any productive work in 1840 by philosophers concerning potential dooms day weapons yet to be created by physicists?
It has been suggested that humans recovered from a population bottleneck of less than 30,000 individuals (the Toba catastrophy). A nuclear war would leave billions alive.
Let's hope that the increased notice taken of AI, and fear thereof, doesn't suddenly shut down a major source of hope for the future.
Poking around a little, I also find this essay, which I think does a better job of getting to the root of the issue: http://edge.org/conversation/one-half-a-manifesto
As the gentleman says, a lack of Autonomous Agents is not the thing standing between humanity and oblivion. The conspicuous surplus of super empowered agents (as in "I could leave this room and 80 million people would be dead 40 minutes later") is.
As for the Royal Society stuff. For the record it's not learning, and it's not the machines, I can say it again if anyone bothers to listen. Although given that it's not what will get news print or sell books or get on telly I am pretty sure that no one will.
Ho hum.
(edited 'cos I forgot a bracket, which was why I gave up c)