Ian,
By accepting that "good" and "evil" are human constructs, and stating that our "belief-systems" are filtered and therefore not absolute (are illusory), aren't you disqualifying Zen Buddhism as well? For, then, is "dukkha" good or evil -- absolutely or relatively? Is Zen Buddhism as a belief-system illusory or non-illusory; if not illusory, on what grounds? In fact, as I understand, Zen would not even consider a rational argument as "real"; therefore, they use riddles and puzzles and talk of transcending logic; in which case Zen is not open to philosophical discourse. But, how does Zen know that what it claims to be reaching is the absolute and the real-- on the basis of experience, reason, or intuition? If Zen claims to be the truth, it is asserting at least one absolute, that Zen is the truth, which is self-contradictory if it claims that all polemic attempts are illusory.