How we cite our quotes: (Part.Chapter.Paragraph)
Quote #1
Now the latter theory, admissible after all, was unable to survive the researches carried out in the Old and New Worlds. That a private individual had at his disposition a mechanical contrivance of this sort was improbable. When and where could he have had it built, and how could he have kept its construction secret? (1.2.6)
Maybe amazing individual achievement is less believable because we don't want to admit that other men are more capable than we are. Aronnax is less willing to admit his own limitations than most; he's too interested in being a renowned scientist.
Quote #2
I would not have been nearly so astonished to discover the most fabulous and mythological of creatures. That what is extraordinary could have come from the Creator, is easy to believe. But to discover all of a sudden a mysterious human construction of the impossible, to find it before your eyes was enough to unhinge your mind. (1.4.69)
Here, again, Man seems unwilling to admit that other men can create great things. Perhaps it's no wonder that Nemo fled "society" for open water.
Quote #3
Where were we? What strange force was taking us away? I felt, or rather believed I felt, the machine sinking down to the furthest depths of the ocean. Fearful waking nightmares tormented me. I glimpsed a whole world of unknown animals sheltering in mysterious refuges, with the submarine vessel as one of their congeners, living, moving, formidable like them. (1.8.65)
Aronnax himself says that it's easier to believe in an unknown natural creation than an awesome manmade one. Here, he backs up this claim by observing that the Nautilus is so advanced, it's like an animal. We're always afraid of what we don't understand, right?