I never said that being ethical means a rigid observance of a code of conduct. It's unethical to steal, but when stealing a loaf of bread is your only way to prevent your own death or the death of others, steal the bread. Cannibalism is unethical, but the same logic applies. If we knew in 1930 what Hitler would do by 1939, would assassination have been unethical? What about assassinating Idi Amin when he was in power?

"The greatest good for the greatest number" is one of the principles which must be taken into account. Which brings us to Utilitarianism, Pragmatism, and a whole bunch of other schools of ethical thought.

I suspect that anyone who held to a absolute rigid code of ethics would either be one of the most horrible dictators who ever lived or wouldn't live very long before someone killed him or her.