Well, slavery WAS legal. And moral or not, men who owned slaves had a huge economic investment for not ending it. The bottom line is that slavery or not, states-rights dictated the right of the states to decide the issue, NOT Abe Lincoln, and a Republican Congress.
No there is not right to own a slave. It is an impossibility and God certainly does not give any of us a right to own another.
As others have mentioned Abe was not going to free the slaves but that didn't matter to the Conspirators who were determined to destroy the Union.