That's the "legal" argument. Not a moral argument. When the southern states seceded, the lost all Constitutional protection as well. Yet southerners gripe about their "rights" being violated. Clearly, Lincoln had not further legal obligation to the seceded states. Yet southerners still bitterly condemn the "immorality."
Can't have it both ways. If legal defines moral, then abortion is moral and anti-abortionists are acting immoral trying to oppose it. Etc etc etc.