“Some killings are justified, some are not.”

"And I would daresay that what one person considers [“justifiable cause”]—He was raping my child; She was having sex with a man not her husband; He didn’t show me enough respect; The baby just wouldn’t stop crying!; She brought shame upon our family—another will not."

Justified – necessary, defensible, right, acceptable, reasonable, warranted – Source Microsoft Word2000 Synonyms

Reasonable is probably a good yardstick here. Would you consider it "reasonable" for someone to kill you because you didn't show them enough respect? Do you think it would be "reasonable" for someone to kill you, particularly as a "baby", just because you wouldn't stop crying?

"As ye would that men should do to you, do ye also to them likewise."