I read the sermon. But I don't believe that was ever the purpose of the Proclamation or that "extinction" was really the word for what was going on. What happened is that the South got outplayed by Lincoln and they were mad about it. They were trying to court the European powers, despite the strong anti-slavery sentiments such people held. By turning the Union army into a liberation army with just a stroke of his pen, Lincoln deftly made it impossible for Europeans to support the Confederacy without it being a public display of putting national interests ahead of their national ideals. That's not extinction. As I said in another thread, Lincoln did not create the sentiments that made the Proclamation so effective. He only recognized that they were sentiments he could make use of to drive a wedge a between the Confederacy and their prospective allies. And it was not like the Confederacy was going to give up the fight at that point anyway. He even provided that option, probably knowing that they wouldn't take it. So, I don't think it lengthened the war or made them anymore determined to fight than they already were. Death ground would have done both.