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.
Huh? In the Constitution the federal government can only do those things the Constitution gives it the power to do. Certain "rights" that are innate in us as humans are explicitly listed to spell out to the federal government that they cannot do certain thaings that interfere with the exercise of those rights. So how can the federal government gain that power to interfere with those rights because some states secede? The federal government cannot establish a religion in the United States but it can in the Bahamas? The United States federal government cannot pass a law to shut down a newspaper in the New York but it can in Manitoba?