Intertextuality and the Discourse Community

In "Intertextuality and the Discourse Community" Porter basically completely opposes Murray's "All Writing is Autobiographical" by saying all writing is taken from "..bits and pieces of text which writers or speakers borrow and sew together.."  or saying everything is loosely plagiarized and not autobiographical.   Porter's argument also argues that his article itself would have intertextualiy, as well as the Declaration of Independence which "...strongly resembles, ironically, the English Bill of Rights of 1689...".  I say that the view points are opposite in terms if their definitions, but are they truly opposites? In terms of where information comes from to be included in an article or writing, they are very similar.  Murray says that no writing is truly objective, that some part of the writing was written or included because of something that happened to the author once, or because of something they read or heard about once, therefore writing about their experiences, or loosely autobiographically.  Porter says that "all writing and speech arise from a single network" or all writings come from pieces of other past writings that an author had read or heard about previously.  The two viewpoints I believe can be taken either way, as opposites in some cases or as the same in some cases.