It wasn't sarcastic. I really think that it's fairly likely to be possible, but extremely difficult. OTOH, I think that many extremely difficult things are worth attempting. That's why SIAI exists after all. LW posters may disagree fairly frequently, but that's probably significantly because there are so few of us that we don't really have time to collectively build an official correct world-view which is far better than any of us could do on our own.

I really do think my claim about the implications of developing such a technique is correct, in fact, understated, and that this follows trivially from the world having resources which are far beyond what is needed to solve its problems if those resources were allocated half-way sanely. A large number of Rokos would definitely be enough to do the job.