Is right wing state propaganda been the most destructive force in human history?

The answer to your question is yes but in the past most outdated beliefs just died out as the world progressed. This time the far right have access to the media and therefore they can keep their long dead ideas around much longer and indeed revive old ones. For example in the last thirty years Americans made Creationism mainstream and have disregarded evolution. Also on a more humours note their has been a revival in the whole Earth being controlled by humanoid Reptillians.