Take some form of consequentialism, precompute a set of actions which cover 90% of the common situations, call them rules, and you get a deontology (like the ten commandments). Which works fine unless you run into the 10% not covered by the shortcuts, and until the world changes significantly enough that what used to be 90% becomes more like 50 or even 20.
The trouble with this is that it contradicts the Reason for Being Moral In the First Place, as outlined in Elizier's metaethics. Said reason effectively comes down to obeying moral instincts, after all.
WHY said morality came about is irrelevant. What's important is that it's there.
My apologies if this doesn't deserve a Discussion post, but if this hasn't been addresed anywhere than it's clearly an important issue.
There have been many defences of consequentialism against deontology, including quite a few on this site. What I haven't seen, however, is any demonstration of how deontology is incompatible with the ideas in Elizier's Metaethics sequence- as far as I can tell, a deontologist could agree with just about everything in the Sequences.
Said deontologist would argue that, to the extent a human universial morality can exist through generalised moral instincts, said instincts tend to be deontological (as supported through scientific studies- a study of the trolley dilemna v.s the 'fat man' variant showed that people would divert the trolley but not push the fat man). This would be their argument against the consequentialist, who they could accuse of wanting a consequentialist system and ignoring the moral instincts at the basis of their own speculations.
I'm not completely sure about this, but figure it an important enough misunderstanding if I indeed misunderstood to deserve clearing up.