Because, really, what a choice there was; what a prodigy of things to be afraid of! the moment that you understood this, really understood it, you lost your anxiety instantly. anxiety was a luxury, a joke you had no room for once you knew the variety of deaths and mutilations the war offered.
the purpose of the paradox in the excerpt is to

D). Highlight the idea that fear can be viewed in different ways.

Explanation:

The paradox is exemplified as the literary device that proposes the statements which are self-contradictory or opposed to the subsisting expectations or beliefs. Such a device offers a collocation of antithetical concepts with an aim to disclose a concealed or underlying reality.

As per the question, the purpose of the paradox in the given excerpt is to accentuate and reveal the hidden meaning that 'fear could be viewed in different ways'('anxiety was a luxury, joke, etc.') that proposes a contradiction to the subsisting belief that sees fear in one single frame. Thus, option D is the correct answer.

my best guess would be: d allusion

makes the most sense