It is really sad when ignorant, misinformed people get a platform to spread their ill founded beliefs.
The south seceded. Nothing immoral our unconstitutional about it. The north refused to remove a military base in the south or accept the secession.
The secession occurred because northern power interests were at odds with the southern power interests over the advantages of large scale farming. 
The north used slavery as a straw man and the south saw it was really about breaking apart the large plantation (think combine today) system that they were unable to compete with.
If the industrial revolution were shifted twenty years back in time there probably wouldn't have been a war and slavery would have died out on its own as cost prohibitive anyway.
Lee and other soldiers were not generally among those who benefited from slaves. They were simply patriots who were believed they were defending their autonomy.