The South wanted freedom. I can not see that the states had no right to secede. It is like a marriage. If one partner wants out, would you say the other has a right to use force to coerce him or her to stay? Of course not. So why would you say the North could use force on the South to make them stay? What is the difference?

And nowadays there is evidence that the South was right. E.g. Portland, Detroit, Chicago, Newark, etc.