I get depressed .....

I agree that the AI will not necessarily feel compelled to continue its own existence (which I think is covered in the article), but the whole point is that it does not have the existence bias of biological organisms, and therefore if set the task of acting in the best interests of biological organisms, it may end all life, before taking itself out.

We should take the ai's word for the fact that the existence bias is irrational, because it is plain to see that no biological organism will regret its non-existence, but will be freed from the cycle of suffering and need. This would be a hard sell, as the existence bias is all consuming for most, but but the ai may decide to save us from ourselves, rather than putting the matter to a democratic vote. There is no need for us to continue existing, only our genes duping us into the belief that continuation of the cycle of life is a beneficial thing.