Do-gooder
Part of speech: noun
Definition: One who advocates or performs what they believe to be the morally superior course of action, even in the face of overwhelming experience or factual evidence that its effect is only irrelevant or harmful.
Humanitarian
Part of speech: noun
Definition: A person with such concerns; a philanthropist or do-gooder.
Part of speech: adjective
Definition: Concerned with people's welfare, and the alleviation of suffering; humane or compassionate.
Example sentence: I do not think that war is always wrong: sometimes it is necessary to stop a dictator, prevent massive human-rights abuses, or expel an invader. But I have also seen that in the modern world, civil wars are the greatest threat to humanitarian security.