“It was property of the U.S. government and secession, even if it had been legal, didn’t change that.”
BS. The South left the union so the union must leave the South. The only reason to stay was to give Lincoln a reason to pick a fight.
BS. Ownership didn't magically change just because South Carolina decided to walk out. Sumter was owned by the federal government, built with federal money on land deeded to them free and clear by act of the South Carolina legislature. They had no legal claim to it. None whatsoever.