Ethical injunctions are rules not to do something even when it's the right thing to do. (That is, you refrain "even when your brain has computed it's the right thing to do", but this will just seem like "the right thing to do".)
For example, you shouldn't rob banks even if you plan to give the money to a good cause.
This is to protect you from your own cleverness (especially taking bad black swan bets), and the Corrupted hardware you're running on.
Sequence by Eliezer Yudkowsky, imported from the wiki. Overlaps with Quantified Humanism and Against Rationalization.