What was Lincoln's great fear in issuing an executive order freeing the slaves?

In this video segment, from the PBS documentary Looking for Lincoln, Henry Louis Gates, Jr. and historian David Blight examine President Abraham Lincoln’s mixed motivations for issuing the Emancipation Proclamation. They conclude that while Lincoln ultimately recognized the moral righteousness freeing the slaves, his first and primary concern was strategic: it was the best way to rally the North and strike at the heart of the South’s economy. Gates and Blight then join a roundtable discussion of Lincoln scholars debating the legal authority of the Proclamation and its special meaning for African Americans.