Says who? Lincoln?
But as long as we are talking legalities, what of the secession of West Virgina from Virgina? The Constitution says no state shall be formed from the territory of an existing state, without the permission of its legislature. Now you would have it that Virginia and the other states of the Confederacy never legally seceded, Lincoln said there was no way they could do so. But it can't be both ways, if the states never seceded, then Virginia was a state, and West Virginia should have been restored to it after the war. And if the states never seceded, why did they have to petition for readmission to the Union? That process was strung out over several years, July of 1866 to July of 1870.
The Union, and particularly those who took over after the assassination of Lincoln, had it both ways. The states were considered to have no longer been in the Union when that was convenient, and their citizens to have been citizens of the US, and thus traitors and rebels, when that was convenient.
I would point out that the greatest "traitors" of all, at least in some peoples eyes, The President of the Confederacy, the members of it's Legislature, and it's senior military officers, were never even formally accused of treason, let alone convicted of it. In fact no one was. Only the commander of the Andersonville prison was charged with "war crimes". The Constitution of the United States was amended to prevent them, the former Confederates, from taking part in government ever again, but many of them did, with permission as provided for in the 14th amendment. That includes participation in the Spanish American War.
This country today would be screwed if the South wasn't still a part of us. This is why I'm most glad they lost.
Yes in the long run it was a Good Thing. But even better would have been for the North not to have forced the issue and let slavery die the natural death it was already headed for. And for the Federal Government to have stayed within the bounds set by the Constitution. There could have been many Constitutional, and peaceful, ways to eliminate slavery, if that were what President Lincoln was really about.
You raise an excellant point. I have always wondered how the cessation of W. virginia was legal.