Quote 4
"Never be of any use!" he replied animatedly. "What makes you believe, monsieur, that these riches must be considered wasted if I collect them? Do you think that it is for my own benefit that I take the trouble to gather these treasures? Who told you that I do not put them to good use? Do you think I am unaware there are suffering beings and oppressed races on this planet, wretches to be helped and victims to be avenged? Don't you understand?" (2.8.75)
Nemo makes sure that Aronnax knows he's not just war-mongering on his own accord. He wants Aronnax to know that he's fighting for the freedom of others. But which "oppressed races" is he talking about? And did these people ever ask Nemo to fight for them?
Quote 5
"Dr. Aronnax," said Captain Nemo, "I will answer you today as I answered you seven months ago: he who enters the Nautilus is destined never to leave again."
"But you are inflicting slavery on us!"
"Give it whatever name you wish."
"But everywhere you go the slave retains the right to regain his freedom! And no holds are barred in how he attempts to do this!"
"Who is depriving you of that right?" replied Captain Nemo. "Have I ever thought of binding you with oaths?" (2.19.52-6)
Even in captivity, Aronnax finds some freedom. Here, he toys with the notion that he is free to escape. But he certainly sits around pondering whether or not to leave the Nautilus for a really long time.