Wrong, certain political parties and groups were pushing this idea. The majority of the South did not buy it, some did. Just as abolition in the North was used to bring people to vote, just as Doyle pointed out that pro-Union politics brought out the vote for Lincoln, the issue slavery protection was used to scare the Southern population. If slavery was the primary cause for secession, then why did the secessionist leaders constantly need to remind the public of this? Because they weren't convinced it was a good idea. Once Lincoln gave them a legitimate reason to secede, federal military invasion, (Lincoln's actions technically dissolved the Union anyway, secession was a forgone conclusion), the slavery pitch was dropped.
I miss Roger, he and I fought a lot, but there was one idea would could agree on. The Union of the states was not ideal, it was a necessary evil, needed for the cause of protection in time of war, the War of Independence. The Union of Northern and Southern states should never had been permenant afterwards. The two cultures never got along and were always political rivals. This is at the heart of the secession movement, both North and South, and had always been from the very beginning.