Whoever advances the claim that it is impossible to definitively reflexively justify a position thereby asserts the very thing that his argument purports to deny: it is once and for all established (so might one reformulate what he is saying here) that nothing can be established finally and once and for all.
But besides this reflexive form of definitive justification there must also be considered a definitive justification in resultative or performative mode. The ebbing-away of humanity is the definitive onto-logical justification of certain ethical principles (i.e. of negative >Utilitarianism or antinatalism). We may look, for clarification of this resultative form of definitive justification, to Hans Schafgans’s “Der letzte Mann von Paris”:
“For centuries, the whole Western world was struggling over the right path to salvation and we continued, deep into modernity, to deal with the legacy of these struggles. Today, however, paths are no longer important because there is no more ‘going’.” (Schafgans) A definitive performative justification is achieved where the last human beings capable of procreation remain without posterity and judge that “it is good that it should be so!”