Well, which is it you intend to attack--rationalism or postmodernism?
The OP uses two terms--rationalism and postmodernism--as if they were interchangeable. They aren't.
'Rationalism' has been around at least since the eighteenth century; American democracy is one of its products. Depending on how one understands the term, one can argue that it has been with us ever since the end of the Middle Ages.
'Postmodernism' dates mainly from the 1970s. That's when it superceded
modernism in general culture. Understanding the distinguishing features of postmodernism calls for an understanding of modernism. The two phenomena proceed from different premises.
The OP blends all this into apple sauce. It quotes G. K. Chesterton as if he had something critical to say of postmodernism. But Chesterton never met a postmodernist. He died in 1936--a decade before the phenomenon was recognized and the term was coined. He was taking issue with modernism.
So which of those things are you really attacking? Is it rationalism or postmodernism?
Could it be your real objection is to neither? Your real quarrel seems to be with
relativism--which is yet another thing.
If that is the case, why not just abandon the other terms and clarify the issues you see involving relativism? There are all kinds of relativism. Which do you have in mind?
The first task is to clarify, in any case.
________________
Edited by Archer Opterix, : typo repair.
Edited by Archer Opterix, : brev.
Edited by Archer Opterix, : brev.