I wonder if the liberals here realize that nearly every argument they make against the Confederacy can be made against the American colonies in the War of Independence--and in fact was made by the British during and long after the war.
Indeed, if the abolition of slavery is the main criterion by which liberals judge wars, then they should wish that the British had won the War of Independence. A good starting point is Alfred and Ruth Blumrosen's book Slave Nation: How Slavery United the Colonies and Sparked the American Revolution (2006).
Tens of thousands of American slaves flocked to British lines after Lord Dunmore offered freedom to American slaves who would fight for the king. Far more slaves were freed by the British than were freed by the Patriots. In fact, after the war, George Washington tried to get the British to return some 15,000 American slaves who had fled to British lines (the British refused).
Before the war, the New England colonies were making fantastic fortunes off the Atlantic slave trade and the British were starting to crack down on slave trading (FYI, most slave ships operated from Northern ports--the two largest slave-trade ports were in Massachusetts and Rhode Island). The pro-abolitionists Somerset decision from the British high court in 1772 sent shock waves through the colonies--north and south.
Leading Patriots who were also slaveholders included George Washington, Patrick Henry, James Madison, Benjamin Franklin, Thomas Jefferson, Samuel Chase, John Hancock, John Jay, Benjamin Rush, and others. (Liberals, I suspect you've never heard many of those names before--you can Google them.)
If the British had won, slavery most likely would have ended by the 1840s or the 1850s, if not sooner.
Yes, the founding fathers acknowledged that slavery was wrong and/or inconsistent with their professed principles. Well, Jefferson Davis, Robert E. Lee, Joseph Johnston, Judah Benjamin, and a host of other Confederate leaders and figures likewise said slavery was wrong and/or expressed hope that it would end sooner rather than later and/or said that they would rather see slavery die than see the South rejoin the Union. Go read some of the Southern newspaper editorials on emancipation when the Confederate debate on emancipation erupted.
After all, as mentioned earlier, by early 1865 the Confederacy began the process of gradual emancipation, after fierce debate in the Confederate Congress and across the South. The debate was so intense because everyone knew that the slave-soldier bill would eventually spell the end of slavery, and it would have done so if it had had time to play out.