If an idea is killed—its value denied, its necessity contested, the books containing it burned—it is still not truly dead. Another mind, in a year, or ten, or one hundred, will consider the problem that led to its birth and find the same idea waiting. If it is killed again, the pattern will continue until the idea is generally accepted to be one of two things: completely wrong and thus forgettable, or completely right and thus necessary. Whichever acceptance it receives, an idea can be reconsidered on the slightest new evidence, and given a new sentence without harm to the idea itself.
If a person is killed—her value denied, his necessity contested, her house burned to the ground—he is dead. That person will never again walk the earth, and her friends will never know another like her. If he is imprisoned, those years of imprisonment are lost to him and to his family. If she is fined, her livelihood is lost, perhaps never to be regained. If a person is killed, even vindicating evidence is not enough to bring him back to life.
Treasure people above ideas. Even this one.
Evil is the willful harming of one human being by another.
Notes:
1) Harming is different from hurting; “to harm” is here defined as “to cause lasting damage to the body, life, or livelihood against the will of the one so damaged”. “To hurt”, in contrast, is here defined as “to cause physical or emotional pain”. Thus, BDSM and assisted suicide do not fall under the definition of harm.
2) A “human being” constitutes any language-using creature capable of understanding the concept of harm or hurting. This may include some apes and/or whales, and certainly includes hypothetical extraterrestrials with those capabilities.
3) In situations where all options will cause some harm or damage, the one that causes the least harm or damage does not constitute willful harm. Thus, a doctor amputating a limb to prevent death constitutes no willful harm.