Toby,

>>You should never, ever murder an innocent person who's helped you, even if it's the right thing to do

>>You should never, ever do X, even if if you are exceedingly confident that it is the right thing to do

I believe a more sensible interpretation would be, "You should have an unbreakable prohibition against doing X, even in cases where X is the right thing to do" - the issue is not that you might be wrong about it being the right thing to do, but rather that not having the prohibition is a bad thing.