Most Southerners fought because the Yankees were invading their states, their cities and towns and creating mayhem in the process.
I remember reading an old anecdote about a Confederate enlisted man who was captured in Virginia.
The Confederate soldier was sitting on the ground under guard when a Union officer walked up to him and asked the Confederate soldier why he was fighting.
The young Southern soldier raised his head and looked at the Union officer as though the Yankee had two heads.
The Confederate soldier looked the Union officer squarely in the eye and answered, “Because you’re HERE!”
Captain Frederick Benteen in the 1879 Court of Inquiry concerning the Little Big Horn matter stated in a different way why men would oppose the blue army which had been given orders to take it all.
“We were at their hearths and homes,” he said, referring to the Sioux . . . “and they were fighting for all the good God gives anyone to fight for.”