Postmodernism, is there an objective truth or is everything a social construct?

"Post Modernists" believe that everything, social norms, religion, laws, etc are created by humans and that nothing is absolute. So, by extensionwe can take these norms and "de-construct" them and rearrange them in any manner we see fit in order toillustrate a different point of view. At first glance this can be very unsettling and can disorient the viewer and even garner a strong emotional reaction, sometimes this is the intent. So what do you think, are there some topics that are off limits to discussion? Is"Post Modernism" worthwhile?