Yeah, it's a real good thing the fed ignores the 10th Amendment. You see, if the states were allowed to decide things like the drinking age and the speed limit, the communist hordes would overrun us in no time at all!
What the critics of Lincoln are saying is that they wish the South had the same right to self-determination that our government has long proclaimed to other parts of the world.
I am not aware of anyone who thinks that the south would ever have volutarily rejoined the northern States in political union, especially after the brutal treatment the north inflicted on non-combatants in the south. As for the eventual abolition of slavery in the south: Slavery had existed throughout the northern States at one time, and had gradually been abolished. It was also peacefully abolished throughout Latin America. There is no reason to believe that things would have ended up any differently in the South.
Any drastic change in history such as the South winning its independence would have greatly altered course of history throughout the world. We don't know the details of what those changes might be, but it is rash to assume that communism and national socialism would automatically have arisen in any event.
And when one considers the terrible course that history has in fact taken the last 140 years (and especially the last 98 years), it is wise and useful to consider how our past leaders could have done things differently to avoid the terrible destruction of lives and liberty that have occured during that time period. Learning from the mistakes made in the past is the best way to avoid the same horrible mistakes in the future.
Wrong. Without a single centralized polity, Germany would certainly have won... WWI. No German defeat, no Hitler. No Hitler, no Nazism. No Nazism, no WWII (not to mention, no Holocaust). No WWII, no Cold War. And if Communism had survived and remained a threat, it would have been mainly a threat to Germany.