In a recent essay, Brian Tomasik argues that meme-spreading has higher expected utility than x-risk reduction. His analysis assumes a classical utilitarian ethic, but it may be generalizable to other value systems.  Here's the summary:

I personally do not support efforts to reduce extinction risk because I think space colonization would potentially give rise to astronomical amounts of suffering. However, even if I thought reducing extinction risk was a good idea, I would not work on it, because spreading your particular values has generally much higher leverage than being one more voice for safety measures against extinction in a world where reducing extinction risk is hard and almost everyone has some incentives to invest in the issue.