That is because we have seen the alternative- and in today's world that means we'd degenerate into mass violence verging on, if not actually encompassing, mutual genocide(s) and civil collapse as we all fight for top spot. That is one of many lessons of history we have seen on multiple occasions- but one that too many neo-nationalists are keen to overlook if not ignore. So go ahead and ask yourself- why would/should/could another round be any different? The biggest difference to my mind now is how far we now have to fall. As a biologist I see it as a short cut to extinction but perhaps I just do not appreciate the glories envisioned by true believers that make it worth the risk.