In the final analysis, I believe that where one stands on the issue is highly dependent on where one places primacy. If freedom is a moral and absolute good, then the war was needed. Southerners viewed their way of life as an expression of freedom that had to be preserved. They were willing to die for this belief, hence war was not something to be overwhelmingly feared. If individuals believed slavery was wrong, they would be willing to go to their own natural ends to prove this. In this setting, individuals were convinced of the moral good in abolitionism and were willing to defend such a belief through any possible means. The reality in both is that convictions are elements of passion, where war in their name can be waged. Ideas and beliefs can be negotiated, but not convictions. If one believes that there were convictions in the formation of the Civil War, then it becomes quite logical to sense war in their name is quite plausible.
If you believe, as many do, that freedom is always preferable to slavery, then the war was worth fighting because it allowed many slaves and their descendents to become free earlier than they otherwise would have. (Therefore their lives improved by the very fact of being free.) If you believe this, you will likely believe that the waste of resources and human lives was worth it because it corrected the great injustice of slavery.
Here's an interesting thought -- could black-white relations now have been better if slavery had ended "naturally?" Would white Southerners have held so strongly to racist institutions if they hadn't been bitter about the loss of the Civil War?
I don't know the answer, but it's an interesting thought exercise.
The Civil War had an enormous effect on industry in the North. As a result, it helped change the U.S. from a country that was farm centered and plantation-centered to one that was mechanical and was reliant on the market system. Before the civil war there was only a small industry in the North. During the summer of 1860, the US had 128,300 companies registered as industry. New York and Pennsylvania the most industry.
On the down side, many of the African Americans who had been slaves went back to work doing the same thing they had been doing before; however they got paid. Not necessarily with money but by obtaining land rights for their modest homes. Howver the playing field was slightly better for African Americans because they had "some" rights. Of course, the later civil rights movement built on the successes of the civil war.
Some African Americans moved to the north where they were treated better than in the south. Since industry had grown there were more jobs there, so their economic situation improved.
On the one hand, wars are never great things, especially civil wars. The loss of life and destruction of property are lamentable. On the other hand, sometimes you need to fight for what you believe in and cherish. One of the things that is necessary to fight for is the rights of people, which means the abolition of slavery. Surely, slavery was not the only issue in the Civil War, but it was a part of the reason. In the light of this, the war was necessary, just as World War II was necessary. Imagine in Hitler won? The world, I am pretty sure, would be a worse place.
Abraham Lincoln articulated in his Gettysberg Address that the Civil War was a test whether this nation could long endure.The Union defeated the breakaway states of the South, and we passed the test. This nation was conceived in liberty and dedicated to the proposition that all men are created equal.