If you're interested in understanding how postmodernism has been subverting meaning, motivating chaos, and how it's married to activism watch this interview:

https://www.youtube.com/watch?v=xILBpDOqD-A

It does a good job summarizing key ideas from Derrida, et. al.

At the end of the day, people are frantically grasping for power by spreading doubt into all modes of communication, institutions, cultural ideas, etc.