The "youth bulge" hypothesis says that whenever the proportion of young men in the population was very high, their unhappiness with their future prospects - i.e., their inability to get jobs and sustain a family and their future - often ended in imperialistic or rebellious movements & endeavours, such as the crusades, genocides, and terrorism.
Historians seems split about this hypothesis as a mono-causal explanation and red thread for human history. I'm partly convinced that the youth bulge might be a necessary, though insufficient condition for imperialistic movements. However, it's hard to build an opinion without historical demographic information.
According to acknowledged historians, what were the main arguments for and against the youth bulge hypothesis? I would appreciate an in-depth explanation of those arguments.