Why did the South consider enlisting slaves as soldiers? What were the arguments against this practice?

Answer 1

"In the first place, by an act of the Confederate Congress, approved February 17th, 1864, there were some thirty thousand or forty thousand slaves drafted into the army as cooks, teamsters, trainsmen and the like, and the soldiers found that they not only got along with them, but that he saved them no end of work and trouble, was handy, amiable, liked the service well enough, and was not without a spirit of adventure."
The argument for: to free up further manpower to fight, since by 1864 the Confederacy was running low on recruits.
The argument against: the South had always feared slave insurrections, and like many in the North, doubted the ability of the slaves to fight.
"The Confederate ***** soldiers never went into action."

Answer 2

For the same reason that the Union enlisted Blacks as troops the need for manpower to fight the war.

The plan to enlist slaves was put forward by Brig General Patrick Cleburn in 1864 his idea was to ask slaves to enlist with the promise to give them their freedom in exchange. This plan was supported by Robert E. Lee and James Longstreet. The arguments against that plan was how would the south survive without Slaves.

Just weeks before the war was ended at Appomattox the South enlisted blacks to fight for the south but at the end they were still in basic training.