I don't know about "fundamentally stupid" but early on in our social development we faced certain problems and came up with ways of addressing them. Food source too rough to chew? Cook it with fire. Conflict between groups? Kill them, or die trying. Despite the problems violence causes, in many respects it has been a potent method and became firmly established in human societies. Even if some groups didn't want to practice violence, they faced the threat of violence for others and the most tangible solution was to prepare to enact violence themselves. As Margaret Mead put it best, if a society has the concept of war and holds it as a possible response for a certain set of criteria, when met with those criteria, they are likely to go to war. Societies without that concept, that don't hold war as a useful response to their problems don't have war. Among the inuits for instance, while they do have some ritualized violence between individuals, killing is rare and they do not have war.
War is useful, particularly for many of the people in power, it is also profitable, again for the elite. It is a long established pattern of behavior that has been passed down from one generation to the next in many different societies. There are cultural pressures and supports for its practice. But we must remember that there is nothing about it that is necessarily natural. It is an invention, a developed and constructed behavior. We still have the ability to develop new solutions to conflict and in many respects we have, but we do not yet hold war as obsolete.
Personally I believe, that whatever the cultural pressures and admittedly myopic tendencies when under the stress of the moment, that it is our capacity for agency in determining our actions, both as individuals and in groups that is best described as the 'human condition.'