I don't think he gave up, he wasn't afraid to fight juubito. He was pissed, because he was thinking what if! what if i fight and win but all these people die or i could stop fighting and they will all live, just inside a genjutsu. He then remembered the sasuke incident when he wanted to call out, should have called out but didn't, he didn't act and look what happened. So in the end he decides to act, he flips juubitos words around, because he doesn't want the regret of doing nothing, of thinking "I should have". He didn't give up, he was deciding what was the lesser of 2 evils, what was the best way to win and he decided to go. Unlike juubito, naruto lives with the pain of losing people he cares about, how many has he lost so far, how much pain has he gone thru and it hasn't changed him. Juubito lost some girl who didn't even like him, but is sooo weak that he cant stand the pain of 1 person dying, so he's willing to destroy the world and hide in his genjutsu lie so he won't feel the pain. Nope naruto didn't quit, juubito did