>Also, his argument has the same short-coming as the "sacrifice" dilemma: We cannot know for sure that a certain action will have a certain outcome - or that any action taken was actually the cause of the outcome.

I don't see how this is a shortcoming.

If I am leading a company, I cannot know for sure that a certain action will have a certain outcome – or that any action taking will actually be the cause of a given outcome. That's not going to prevent me from doing my best to build a good product and make a profit.

In the same way, the uncertainty inherent in reducing existential risk shouldn't prevent us from doing our best to reduce it.