Unfortunately, humans do often get excited about warfare, particularly in the early stages. World War I and the Iraqi invasion in 2003 are good examples. Once reality sets in, then the population steps back on a "maybe this wasn't such a good idea" footing. It's just a typical human reaction when something big is about to happen. I don't think it reflects too badly on our nature, especially since most of the time we have the sense to recognize that war is mostly, but not always, a pathetic adventure.