Why? If Carton is going to say that Lincoln knew beyond a shadow of a doubt that his actions would provoke war then why is it 'false dilemma' to ask for his evidence? And when all he can offer as proof is his opinion and his opinion only the it's hard to take him seriously.
Because the form of your proposition was, and is, entirely a "false dilemma", that's why.
You're as phony as a used-car salesman, so spare us the injured innocence.
Either A, which I know isn't forthcoming, or B, I get my way on the point I need to support "it was all about slavery/South 'rebelled'".
Phony as a three-dollar bill.