This is a linkpost for http://vif.fitnessism.org/2016/08/reasonable-requirements-of-any-moral.html
The author is far from alone in his view that both a complete rightness criterion and a consistent decision method must be required of all serious moral theories.
Among hedonistic utilitarians it's quite normal to demand both completeness, to include all (human) situations, and consistency, to avoid contradictions. The author simply describes what's normal among consequentialists, who, after all, are more or less the rational ones. ;-) There's one interesting exception though! The demand to include all situations, including the non-human ones, is radical, and quite hard a challenge for hedonistic utilitarians, who do have problems with the bloodthirsty predators of the jungle.
Among hedonistic utilitarians it's quite normal to demand both completeness
Utilitarianism provides no guidance on many decisions: any decision where both actions produce the same utility.
Even if it is a complete theory, I don't think that completeness is demanded of the theory; rather it's merely a tenet of it. I can't think of any good a priori reasons to expect a theory to be complete in the first place.