I think you’d be very hard pressed to find anyone claiming that the North started out to free slaves. That was a happy result, not their cause. On the other hand, those that claim slavery wasn’t a cause for the south are a dime a dozen and their argument is a fantasy.The problem with running out the "slavery had nothing to do with the war" myth or not, is that there are very few people who actually propose it today. There is of course the Southern Lost Cause myth that emphasizes states rights instead of slavery, but even these omit the idea that "slavery had nothing to do with the war".
On the other hand, there is a Northern myth that rarely comes under such close scrutiny -- that the Civil War was all about freeing the slaves. The Glorious Cause of Freedom or as Lincoln said, " a new birth of freedom". It clearly was not and this is equally false. The proximate cause of the war was the secession of the Confederate states. Ending slavery was never a war aim of the Federal Government. Even the Emancipation Proclamation was used as a war measure to weaken the South because to do more would have damaged the Federal war machine.
Today some of the pillars of the “Old Southern Culture” can make readers cringe: aristocracy, bigotry, secession, confederacy, and, of course, slavery. Importantly, uncomfortable antebellum characteristics were not confined to the South. The North, the Midwest, the Far West, and the Border States all evidenced their own unique characters in this period — many of them no longer acceptable to modern society and opinion: greed, exploitation, nativism, religious intolerance, and perhaps the worst — a lack of restraint. Most Northerners were racists, and they treated even black freeman with brutality when they did not ignore them. They did not want them in their communities except as servants, drudges, and laborers. By these standards many of the heroes of the last century were not very nice people.
Although the questions of slavery or abolition stood out at the time, Southern nationalism was fueled not only by the endorsement of continued slavery, but also by a growing contrast between a conservative Southern culture rooted in agriculture and a progressive Northern industrial society increasingly in favor of popular suffrage, a changing role for women, widening democracy, and social reform. While there remained a strong belief in American individualism, personal strength of character, and the ability of a man to overcome the handicaps of his environment, such concepts were identified more and more with Southern resistance to social reform. A tone of condescension and disdain even entered the rhetoric of the Northern reform movements. Failing to acknowledge any good in Southern society because it was tied to slavery, Northern reformers made no attempt to hide their universal disapproval of all things Southern.