Earlier quoted context omitted.
> What is a "fact" or what is "true" in dependent on your values (aka your ideology). This is one of Nietzsche's main contributions to philosophy. No, it's not. That's one of the Enlightenment’s many contributions to philosophy and the foundation on which the advances in knowledge of the universe enabling the explosion of post-Enlightenment technical progress is built. Obviously, one might have ideological, aesthetic…
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Leninism and it's descendants are totalitarian, Communism (even Marxism) more generally is not, but, sure, you can certainly make the case that scientific rationality has some connection to Marxism and thus an indirect effect on Leninism. OTOH, scientific rationality and the proven results are also the explicit basis for the widespread Western rejection of Leninism and it's descendants (and explictly cited as such by wide segments of the Right, including those who generalize that rejection to Communism generally, which the left might argue is an overgeneralization, but even in that argument there is a broad consensus that there are actual material facts that one can draw conclusions about from material evidence which transcends ideology when approached correctly.)
OTOH, Nazism was not based on scientific rationality, except as a reaction against it, and in fact both Italian Fascism and Naziism were explicitly based on the exact Nietzschean view that you advance (both the idea and explicitly crediting it to Nietzche).
> Postmodernism hinges on whether or not there is an objective set of values. Conservatives believe there is (the Bible, natural law, God, etc) whereas Postmodernists believe there isn't.
That may be a difference between your particular worldview and postmodernism, but large number of other conservatives criticize the “postmodern left” not merely for rejecting objective values which you claim is the difference between Conservatism and Postmodernism, but for rejecting objective facts and viewing facts as constructs which depend on ideology—the position you take on the nature of facts is one explicitly rejected and criticized (and attributed as a failing of the left) by most mainstream conservative thinkers, though I will agree that the factions of the Right who adhere to it are at what is, at least, a recent local maximum of prominence.