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Some people believe that morals are “given to one”. That is, that you adopt a moral code developed by others, such as those prescribed by various religions. To those people, moral values are objective; they’re often written down and subscribed to by entire groups.
To those people it is inconceivable that others can consider themselves “good people” when they develop their own (subjective) moral codes, and even worse when they modify those codes and values as they mature or as their values change.
To answer the question you posed to @Blackberry, “harming another person” can be a moral act at times. If someone threatens my family, then you may be sure that I would have no aversion to “harming” or killing that person. In fact, it would be considered a moral act by most, I suspect.