Friend is a confederate south supporter

I think you may be overreacting, a difference in opinion over a 150 year old event isn't a friendship destroying issue. Now, as a history enthusiast I do want to point out:

Technically speaking, he is right that it wasn't about slavery itself. It was about southern states wanting the right to keep or get rid of slavery for themselves instead of being forced one way or the other. Although they all wanted to keep slavery.

People are under the impression Lincoln and the north wanted to free the slaves, when in actuality they only wanted to free the slaves owned by the enemy to help them win the war. Proof is the original version of the Emancipation Proclamation stating only slaves in enemy controlled territory would be freed (because some allied states supporting him like Maryland also had slaves, and would not have been pleased with him taking them away). While Union slave owners would be permitted to keep their slaves.

 

Your friend is right.
The Civil War began as a defining moment that interpreted the amount of free expression each individual state was to be allowed to entertain and remain part of the Republic of the United States.
The most prevalent issue came down to each individual states right to allow the possession and ownership of human beings by individual citizens.
Most Confederate citizens, by proxy, did not actually fight for their right to own slaves as most were poor dirt farmers themselves who owned very little in the way of material possessions and were unlikely to rise high enough in wealth and status to ever actually own slaves of their own but the thought was there in theory. Instead they fought for what they considered the southern right of autonomy to choose.
In other words, they ended up fighting and dying for the right of wealthy southern democrats to own human beings as chattel.
Those same wealthy southern democrats made claim that their way of life provided jobs and housing for the most underprivileged in their state. (Translation, everyone that wasn't wealthy, oh, and they would have owned the white people too but that had already been deemed illegal years before the Civil War ever happened)
In fact, had the South WON the Civil War the southern democrats in control would have made the enslavement of ALL poor people of any race legal under their intended system of capitalistic government.