How does Thoreau justify the moral need for civil disobedience? What principle does he rely on this justification? 

        According to Henry David Thoreau, civil disobedience is justified when the government is unjust. That is, when it physically controls civilians without allowing them to follow their conscience. Thoreau bases his essay on what he experienced in his country. He was supposed to pay his annual poll tax, but he refused to pay because he did not want to take part in The Mexican War and in enslaving. 

A thought on behalf of a nonconformist ...

        A self-reliant man would disagree with most of the modern day aspects because they make people conformists. The most effective aspect is the media. In a unique man's point of view, media  is a destructive element of one's undiscovered ability. People would want to behave like a certain actor or dress like that singer or starve themselves to look like a particular model. This is how media manipulates the inner good-will of a human being. Even though a non-conformist  disagrees with most of what the media produces, he still might agree with a few. He would definitely agree T.V programs that encourage talents or inventions because these shows make people discover what they're capable of.