Well, I don't see how loser is a moral measurement seeing how even had the south one and there had been winners, they'd still have been slavers and traitors.
On second thought, even traitor is not necessarily a moral standard. After all, members of the German resistance to Nazi rule would have been traitors to the regime too. Sometimes committing treason could be the moral choice. But they're still slavers.
And the United States was founded on treason.