Answer:
The basic answer for the South was the fact they needed and wanted to maintain slaves to keep up with the demand for the goods grown in the South.
The North, however, turned a blind eye to the fact all the clean cotton that was purchased and used throughout the mills was actually from the southern plantations where Slaves were actually used.
This was easily overlooked by the introduction of the fear that the slaves when released in the South would make their way to the North and compete and take the jobs from the locals.
Step-by-step explanation:
Throughout all of history, there have been slaves or some class that fills the role of slaves. Egyptians enslaved the Jews, Romans enslaved those they conquered and the kings of Europe had serfs throughout the middle ages. The ghastly act of selecting a group of people and forcing them into labor none wanted to do in order to save costs and resources has been a stain on human history. So when the United States brought slavery to its shore unfortunately it wasn't something new to the world. After the Resolutory War, the American economy was in shambles and it needed a cheap workforce to stimulate its economy with the production of its agricultural goods.
This is where the North and South were divided in the US. The North's main exports came from factory work and their towns turned into modern cities of that era. While the South still held onto the farmlands and more rural traditions. Slavery was considered a necessary evil due to cotton being such a huge export up until about 1830 with the growing abolitionist movement in the North. The Southerner's justification for slavery started to lose its credibility as the call for its end grew louder and louder. Soon the slave owners were justifying slavery for numerous reasons such as offering better living conditions than those found in the Northerner's factories or a more religious base such as Abraham from the bible also owned slaves.
Regardless of their justifications and their attempts to change their view to a "Positive Good" their reasoning was based on fear and greed. Many of them thought that the abolishment would destroy their economy with the loss of products and jobs. Since some slave owners could hardly make a living without having to pay their slaves they saw a grim horizon of financial deficit. This is the reasoning told to themselves in justification for their actions. Their ideologies resided on their finances and continued way of life and that is why their views changed from seeing slavery as a necessity to justifying it as a positive good.