Union was wrong, but that doesn't make South right. Especially when one looks into what South did during the war.
Ideally Union could have been maintained and Slavery abolished, Tariffs repealed, and Free Trade rained supreme. Unfortunately, not sure that this was possible.
If South was allowed to leave without any problem, I am certain that North and South would have fought a war within short period of time. The problem then would be that South would likely have gotten support from Britain and France.
The whole thing makes Civil War a very complicated time in history of US, and not black and white like we make it seem today.