I believe I can show that the criticism of post-modernism is not necessarily the misinformed scapegoating you have presented it to be. More specifically, I will single out the most contentious claims that commonly carry the label of post-modernist.
1.In the final analysis, the structures at the core of Western civilization are predicated on power alone. — This is shattered by a single example: The British empire ended the Atlantic slave trade at a great cost of lives, time and resources. However, if that is not enough, power without responsibility and without meritocracy is tyranny and tyrannies tend to fall apart from the inside rather quickly. If that claim were true, no one living in the West today would have any rights.
2. There is no such thing as human nature based in biology, a.k.a. the tabula rasa (or blank slate) conception of the human being at birth. In other words, culture is the only determining factor in a person’s development. — The whole field of evolutionary psychology is a testament to the falseness of that claim. It’s not nature versus nurture, the two are in a constant feedback loop. Denying the fact that evolution has played a huge part in the formation of not only our physical bodies, but also of our psyches is no different that creationists claiming the Earth is 6000 years old.
3.There is an infinite amount of ways to interpret reality, therefore no single one of them is more valid than any other. — The first part of this claim is true, considering what we know about neuroscience and artificial intelligence. However the second part is absolutely false. There are a huge number of constraints on which interpretations of the world are valid — all those that would get you killed in no time are automatically invalid; all those that would preclude you from ever coexisting with other human beings are invalid, too; all those that serve no practical purpose for life are invalid. Ethics and Darwinism both constrain the number of valid interpretations of the world to very few.
4. All groups — differentiated by race, gender, sexual orientation, etc. — are in a constant conflict for power with each other. — This claim can’t actually be truly post-modern, considering the one above, because it is a very particular (and subtly Marxist) worldview, but thinkers such as Derrida have advanced claims of this nature despite contradicting the infinite number of interpretations.
5.All dialogue between individuals arbitrarily in different power groups (as defined in point 4) is just a power game between the groups. — I don’t know how anyone can take this claim seriously, but it is a justification used by political activists almost exclusively on the far left to shut down speeches and lectures by those they disagree with — “Hate speech is not free speech.” Instead of debating their political opponents, they try to prevent them from speaking.
6.The concept of dialogues between individuals attempting to get closer to truth is non-valid, because there is no such thing as individuals and no such thing as truth. — There are two very important claims here. The first is that all identity is group identity and that no individual identity can be considered valid. In other words, you are your race, your gender, your sexual orientation, you “oppressed status”, but not an actual individual. The “there is no such thing as truth” claim is more akin to “what we call truth is what those with power call truth”, which completely disregards formal logic and the scientific method.
7.Personal experience, sensation and emotion are as epistemologically valid as reason, the scientific method and analytic philosophy in general. — Essentially, if there is no truth, but that of those in power, we can claim anything is true and no one will be able to tell, so why bother with logic, science, rigor, repetition, experimentation or any way of validation.
Excuse my lack of philosophical rigor on the subject, but the way you wrote your essay implied to me that you assume most of these claims to be valid. I hope that clarifies some of the critiques of post-modernism.