The problem here seems to be about the theories not taking all things we value into account. It's therefore less certain whether their functions actually match our morals. If you calculate utility using only some of your utility values, you're not going to get the correct result. If you're trying to sum the set {1,2,3,4} but you only use 1, 2 and 4 in the calculation, you're going to get the wrong answer. Outside of special cases like "multiply each item by zero" it doesn't matter whether you add, subtract or divide, the answer will still be wrong. For example the calculations given for total utilitarianism fail to include values for continuity of experience.

This isn't to say that ethics are easy, but we're going to have a devil of a time testing them with impoverished input.