Southern Army complicity in its own demise started when the first shots were fired at Ft. Sumpter.
The political objective was independence. How shooting at a much better armed adversary with a much larger population forwarded the cause of southern independence is a mystery.
General Longstreet implored General Lee to vacate Gettysburg and march the Army of Northern Virginia on Washington DC. This appears now to have been sound reasoning as DC was roughly 90 miles from where they were. Had they done that, I suspect there might have been a wholly different conclusion to the conflict. Northerners stood in abject fear of an incursion into the Capitol and subsequent movement north through a southern sympathetic Maryland.