Let me start of by saying, I like both sides. I live in Virginia but was born in New England. Neither side was evil. I feel that both sides need to be remembered and honored equally.
I don't usually get into these arguments, but I will just say this.
The south seceded for many reasons but slavery was definitely a major one.
"Its foundations are laid, its corner- stone rests, upon the great truth that the negro is not equal to the white man; that slavery subordination to the superior race is his natural and normal condition. This, our new government, is the first, in the history of the world, based upon this great physical, philosophical, and moral truth." - Alexander Stephens Vice President of the Confederacy.
The Confederacy was about slavery. There is no arguing that. However, I would say that there were many other reasons that the common soldier was fighting and slavery could have been one of them. (I would say that a lot were fighting for their homes.)
The war, however, was simply about preserving the Union. The Emancipation Proclamation was to prevent British/European intervention. Britain would never step in to defend a country that supported slavery.(The Confederacy.) Therefore, Lincoln decided to turn it from a war to preserve the Union into a war over slavery.
There is still the need to honor the confederates though. They were brave men who fought for something they believed in. I personally feel that it dishonors them when people deny what the confederacy stood for. They were brave enough to die for it which is nothing to be ashamed of.
As for who do I support, I would say the Union. The south's government failed one of it's main goals. It was supposed to have a weak federal government and strong state government. Unfortunately, they had to create a stronger national government in order to survive. Things like the conscription act kind of contradicted this. Which basically says that the national government of the confederacy could force people in the various states to join the army. The same problems came up during the Revolution when America was a confederacy.(Under the Articles of Confederation.) That is why they wrote the Constitution which gives enough power to the national government to function but still protects the rights of the states.