An important confusion to avoid is to think that rule-consequentialism’s including a “prevent disaster” rule means that rule-consequentialism collapses into practical equivalence with maximising act-consequentialism. Maximising act-consequentialism holds that we should lie, or steal, or harm the innocent whenever doing so would produce even a little more expected good than not doing so would. A rule requiring one to prevent disaster does not have this implication.  Rather, the “prevent disaster” rule comes into play only when there is a very much larger difference in the amounts of expected value at stake.