Hitchens make a classic error of moralists: he extrapolates his moral position onto others and grades them based upon that supposition. Not only is in error, it makes him a bad liberal as he should be a champion of moral relatavism which necessarily doesn't judge other people, but tries to understand them for what they are. But, then this flies in the face in his natural contradiction of political correctness. Such is the struggle he goes through. Luckily, this issue is resolves more readily using a rational thought process.
First, Southerners did not love the blacks. Neither did the Northerners. Southerners were content to keep blacks in bondage. Northerners were just as glad the Southerners did so. Lincoln had no issue with slavery, or to interfere with slavery (read Lincoln's first inauguaral address, the history of Hampton Peace Conference, for starters).
Lincoln's stated aim (again his first inaugural address, found on Yale's Avalon site) was to keep the tariff intact, which Southern states paid darn near most of, as they were the major importing states. Without the tariff, the federal governement was essentially financially paralyzed. Southern states resented that they were essentially supporting the federal government (this is a big issue, please do your own due diligence and read about this). They essentially advanced the same political theory that was espoused by Jefferson in the Declaration of Independence that it is the right of free people to break the bond of political allegiance with any government that no longer serves its interests. Lincoln essentially negated that natural right in his offensive against the Southern states.
If Lincoln was correct, then Jefferson must have been wrong. If Jefferson was right for the Union, then the Southern sessionists had to have been just as right. If slavery invalidates the Southern secession, then it necessarily means that it invalidates the colonial secession from the British Empire. Both were, at their core, tax protests.
Ron Paul makes an excellent point that the US was the only nation to get rid of slavery though a civil war. Other nations had the ability to end slavery though legislation. I guess Lincoln wasn't the diplomat that his eloquent words tend to suggest.