Can a human prove anything to be "justified"?
Like breathing the atmosphere?
"Need" is just a fiction. As is "should", "must", "value" and "importance".
You appear to be a rank sophist who doesn't have a point. No one speaks of need without a context. I said such in the first statement I posted. That doesn't make it a fiction. You made the assertion that needs are a fiction, and hence no one needs to do anything. By saying such you've already presupposed the invalidity of the entire concept and the definition of the word itself. But your claim is incoherent because you perpetually beg the question in vicious regress.
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I want a unicorn. http://www.youtube.com/watch?v=w1MKQbNPkgU