Actually that quote should be attribted to the screenwriter for "Gettysburg" because that's were it came from. I've never seen any evidence that Longstreet himself never said anything like that in any of the biographies I've read.
A quote attributed to Longstreet comes to mind;
‘We should have freed all the slaves, THEN fired on Ft Sumnter.’
‘Actually that quote should be attribted to the screenwriter for “Gettysburg” because that’s were it came from. I’ve never seen any evidence that Longstreet himself never said anything like that in any of the biographies I’ve read.’
He got it from Shara’s “Killer Angels” upon which the movie was based. Like you, I’ve never seen it attributed to Longstreet in the various bio’s...but then again, til recently all the bio’s available were the result of those clinging to Ewell and Early’s ‘Lost Cause’ scenario they promoted at the expense of Longstreet, and deified Lee and Jackson.
I’ve wondered if Colonel Fremantle’s book on the Civil War mentioned anything about it, since its alleged the quote was made to him.
Bottom line is the notion has quite a bit of merit in my opinion. Had the South done this first, no ‘emancipation proclamation’ would have occured, and Lincoln wouldn’t have had that era’s version of ‘evangelical’s’ to call on against the congress grown weary of the war.
Just my opinion.