You will notice that about every time one of these NPS/Slavery discussions is printed, one name appears on the side of promoting and advocating the importance of slavery in the context of the Battle. That is Eric Foner, a history professor at Columbia University. If you have read his books, most notably "Reconstruction" you will detect the same theme.
One other example of Professor Foner's "objective" view on slavery and its place in our history may be found at http://query.nytimes.com/gst/fullpage.html?res=9F05E1D91538F936A25752C1A961958260&sec=&spon=&pagewanted=all Note, in particular his discussion with his 9-year old daughter.
In my view, in this same NY Times article, Edward L. Ayers of the University of Virginia had far more enlightened, on-spot ideas on how to integrate (pardon the unintended play on words) the black man into the Gettysburg exhibits.