The Romantic Fallacy is a term coined by Robert Ardrey. He used it in reference to the revolution in the natural sciences that started in the first third of the 20th century. Briefly, the Romantic Fallacy is a scientific frame of reference that sprouted chiefly from Rousseau and his Renaissance-era hoodlums - the idea that mankind is inhererently good.
The roots of this concept date back to the hierarchy of species and early Greek philosophy. (Please remember that a lot of early science--Western science, that is--was the work of Christian monks.) Its effects are still with us today. The logic works like this: Humans are inherently good, friendly and peaceable. Therefore, the evil that we perpetrate is the result of something else. The chief scapegoat for humanity's evil is civilization, and wars are the result of the efforts of munitions manufacturers.
There was once a generation of anthropology professors who insisted that mankind's goodness could be seen in those primitive societies who lived at the corners of the earth: The Eskimo, the natives of Tierra del Fuego, the Australian Aborigine. They were almost uniformally nonaggressive, not prone to thievery or murder or war. Karl Marx must have absorbed this notion as chip-truth -- do away with private property, and humanity's goodness will establish a utopia. Freud could also be identified among this group of thinkers, likewise Thomas Jefferson with his freemason libertine ideas of how a state governed by its citizens should run.
With a little thought, you can probably see the tendrils of this idea in any field of study you care to pursue, and it is the result of sublime logic applied to a false premise. The Romantic Fallacy met its first opposition in the early 20th century with the notion that mankind had sprung not from peaceful, thoughtful monkeys with big brains, but from nasty little club-wielding predator australopithecines, pack hunters, warlike little goblins who fought each other for territory. Our brains, then, resulted from improvements in weapon-swinging ability, hand to eye coordination, the skills of hunting and warfare, and the fact that nonaggressive civilizations were pushed to the edges of the Earth adds another nail.
Religion aside, the notion that humanity is inherently warlike, aggressive, AND prone to civilization has gained impressive footing in a short time. For references to that effect, see The Lord of the Flies or Heart of Darkness, and my sources for this information, African Genesis and The Mismeasure of Man. The scientific revolution rolls on like a ball, showing only half its face at any one time while grinding the other half against the ground.