Instead of quoting the America hater Dickins, you’d do better looking at a contemporary Englishman, John Stuart Mill.
“...what are the Southern chiefs fighting about? Their apologists in England say that it is about tariffs, and similar trumpery.” Yet, Mill noted, the Southerners themselves “say nothing of the kind. They tell the world … that the object of the fight was slavery. … Slavery alone was thought of, alone talked of … the South separated on slavery, and proclaimed slavery as the one cause of separation.”
Might as well quote John Brown. John Stuart Mills was a natural law theorist, and abhorred slavery, and he wasn't interested in doing anything other than condemning it. I also don't see where he visited the US during the time in question, as did Charles Dickens.
Mills was just repeating what all the elite social set of New York was telling him on their visits to England, and what he wanted to believe anyways.
There was a lot of that going on. Still is.