Ultimately... his theory taken as an absolute rather than a generalised trend seems a little simplistic. The idea of actually obtaining rather than constantly pursuing perfection is rather naïve, and while I am a big fan of rationality, humans are fundamentally more complicated than that and emotive reasoning will likely continue to be a factor for better or worse.
Not to mention that there are plenty of conflicts in the world that have neither resulted in a new belief wholly supplanting an old one, nor any established ideas seriously being challenged. Indeed the new status quo seems to be endless stalemates...