People self-justify their actions in the moment without needing to explicitly give thought to moral and ethical factors. Even in your example, the self-justification would be something along the lines of it not mattering anymore because he was going to suicide. In that scenario, the gap between 'taunt' and 'murder' would be filled with the factors that made him suicidal to begin with, and I would give those factors greater weight to the end result than mean words had.