RE: The Declaration of Independence laid out the arguements in favor.
I believe that author is aware of the declaration. His entire argument (academic of course) is that the declaration was not necessary.
When in the Course of human events it becomes necessary for one people to dissolve the political bands which have connected them with another and to assume among the powers of the earth, the separate and equal station to which the Laws of Nature and of Nature's God entitle them, a decent respect to the opinions of mankind requires that they should declare the causes which impel them to the separation.
OK. But Jefferson was a polite man.