Oh, they meant a lot of things at the time. And a lot of what you quote comes under the heading of emotional propaganda, voted by angry Legislators, tired of being insulted by people who were supposed to be their fellow Americans, bound together by ties originating in the Revolution and the building of a Federal Union. But the precipitant for all of the venom on both sides, came from the Abolitionist attacks upon the South, the Constitution itself, etc..
Historians can certainly debate, whether the South over-reacted. But the Abolitionists precipitated the horror which followed. Before the Abolitionist movement gathered steam in the 1830s, Southern leaders openly discussed ways to end slavery. One of the reasons for recommending that you read the Webster speech is that he covers just that point. Practically no one thought slavery a good system, before the Abolitionists began to smear the honor of the Southern leaders.
William Flax