The Union had the right to withdraw its forces from Ft. Sumter. It had no right to wage total war, or to make the return of the Confederate States to the United States into an object of war.
Why should they withdraw? It was federal property.
Nor did the Confederacy have a right to fire on a Federal Fort or issue letters of Marque against United States flagged ships.
Of course it had the right to wage war to protect itself.
Your linking the decline of the US to Roe v Wade is silly. If you are that concerned about persons not being allowed to be treated like persons then you should have link to March of 1857