Clearly Johnny Reb was not as confident that slavery would always be legal. They said otherwise in their secession documents.
Do you know what "circular reasoning is"? Here is your version.
"Johnny Reb went to war to protect slavery."
When it is pointed out to you that not only did slavery need no "protection" but all the main players were offering them even greater protection for it, you respond:
"Johnny Reb didn't believe it."
You are still stuck on that brainwashed position of the only reason for the war was slavery, and you reject any other explanation than the one you have been taught all your life.
You advance your premise of "it is only about slavery", and then when evidence is shown to you that it really wasn't about slavery, you dismiss it because you must insist the war was only about slavery.
Your mind goes round and round in a circle with one part justifying the next part which justifies the previous part.
The war was not about slavery. It was about economics and hatred for the other side.