Fein's points are centered around those comments made by Alexander Stephens and others who had a pecuniary interest in the "peculiar institution." He cites the Confederate Constitution which is not all that different from the United States Constitution--- and actually has some improvements over the original--- but he leaves out the critical point that both banned the importation of slaves. If slavery was something that Stephens and others were so intent upon preserving ad infinitum, then why leave the door shut to importation?
In today's world it is quite common to find people who believe that slavery was the sole reason for the Union invasion of the Southern states. What these folks fail to grasp is that those who owned slaves were concerned that if the institution was ended without some protections for themselves and their charges, that it would result in economic hardship and societal turbulence for decades to come. William Wilberforce campaigned for a peaceful solution to the issue of slavery within the British Empire with no harm done either physically or financially to its subjects. Sadly, no such campaign was waged here other than a military one--- that devastated the whole of the South--- the results of which we are suffering under to this day.
Nevertheless--- and this has been said many times--- the Lincoln Administration was not interested in slavery as war aim at the onset as they were primarily concerned with maintaining the Union. The actual fighting centered around the matter of secession as a right of states and not really anything else.