Ultimately, when you can't compute the right answer in the given time, you will either have no answer or compute a wrong one.
But if the question is possibly important and you have to make a decision now, you have to make a best guess. How do you think we should do that?
It was definitely important to make animals come, or to make it rain, tens thousands years ago. I'm getting a feeling that as I tell you that your rain making method doesn't work, you aren't going to give up trying if I don't provide you with an airplane, a supply of silver iodide, flight training, runway, fuel, and so on (and even then the method will only be applicable to some days, while the pray for rain is applicable any time).
As for the best guess, if you suddenly need a best guess on a topic because someone told you of something and you couldn't rea...
Just a minor thought connected with the orthogonality thesis: if you claim that any superintelligence will inevitably converge to some true code of morality, then you are also claiming that no measures can be taken by its creators to prevent this convergence. In other words, the superintelligence will be uncontrollable.