Surely building an anti-natalist AI that turns the universe into inert matter would be considered unacceptable by most people. So I'm confused.

Yet I am not secretive about it and I believe that it is one of the less horrible strategies. Given that SI is strongly attached to decision theoretic ideas, which I believe are not the default outcome due to practically intractable problems, I fear that their strategies might turn out to be much worse than the default case.

I think that it is naive to simply trust SI because they seem like nice people. Although I don't doubt that they are nice people. But I think that any niceness is easily drowned by their eagerness to take rationality to its logical extreme without noticing that they have reached a point where the consequences constitute a reductio ad absurdum. If game and decision theoretic conjectures show that you can maximize expected utility by torturing lots of people, or by voluntary walking into death camps, then that's the right thing to do. I don't think that they are psychopathic personalities per se though. Those people are simply hold captive by their idea of rationality. And that is what makes them extremely dangerous.

Do you intend to denounce SIAI if they do seriously consider this strategy, and also if they don't?

I would denounce myself if I would seriously consider that strategy. But I would also admire them for doing so because I believe that it is the right thing to do given their own framework of beliefs. What they are doing right now seems just hypocritical. Researching FAI will almost certainly lead to worse outcomes than researching how to create an anti-natalist AI as soon possible.

What I really believe is that there is not enough data to come to any definitive conclusion about the whole idea of a technological singularity and dangerous recursive self-improvement in particular and that it would be stupid to act on any conclusion that one could possible come up with at this point.

I believe that SI/lesswrong mainly produces science fiction and interesting, although practically completely useless, though-experiments. The only danger I see is that some people associated with SI/lesswrong might run rampant once someone demonstrates certain AI capabilities.

All in all I think they are just fooling themselves. They collected massive amounts of speculative math and logic and combined it into a framework of beliefs that can be used to squash any common sense. They have seduced themselves with formulas and lost any ability to discern scribbles on paper from real world rationality. They managed to give a whole new meaning to the idea of model uncertainty by making it reach new dramatic heights.

Bayes’ Theorem, the expected utility formula, and Solomonoff induction are unusable in most but a few limited situations where you have a well-defined testable and falsifiable hypothesis or empirical data. In most situations those heuristics are computationally intractable, one more than the other.

There is simply no way to assign utility to world states without deluding yourself to believe that your decisions are more rational than just trusting your intuition. There is no definition of "utility" that's precise enough to figure out what a being that maximizes it would do. There can't be, not without unlimited resources. Any finite list of actions maximizes infinitely many different quantities. Utility does only become well-defined if we add limitations on what sort of quantities we consider. And even then...

Preferences are a nice concept. But they are just as elusive as the idea of a "self". Preferences are not just malleable but they keep changing as we make more observations, and so does the definition of utility. Which makes it impossible to act in a time-consistent way.