That was a typo. The statement should have read "then why DID the secessionist leaders constantly need to remind the public of this"
"the horrors of freeing the slaves, of them (slaves) becoming judges, jurors, marrying their Daughters...it was a scare tactic used to polarize the Southern population into action."
It really didn't work. Mainly because Southerners, unlike Northerners who DID believe this mindset, knew better. The largest population of free blacks in the United States already lived in the slave states in 1860. Free blacks in Louisiana had an average net worth higher than the average white person in the North. Before 1860, free blacks were allowed to vote in Louisiana; Natchez, Mississippi had several free black business men who operated trading operations on the Mississippi River. This scare tactic didn't work in many parts of the South. Slave or free, Southerners knew in the 19th Century, that they would never allow a radical change in the social order, so they really weren't scared into secession by such ideas. But they did secede, especially after Lincoln's actions, they seceded in mass.
In the early part of the secession, slavery was put forth as ONE of the rights that would be lost under a Northern, abolitionist, Republican govenment. It was a constant with the radical secessionist pushers. The effect was not overwhelming, nor postitive for the movement. Money controlled most of the governments in the deep Southern states and with it the power to put forth a rowdy and successful showing, but the majority of the population of the Southern people were not fully behind this political idea. Add to these the real feelings of the people in Alabama, Mississippi, Texas, Louisiana and Florida, who were never in love with being in a Union with New England and vise versa. This hatred had all to do with culture and social order between the geographic populations of North and South. These deep Southern states were new to the Union and change in government to them was not a new idea. They had been colonies and territories in the European empires of Spain, France and England and with Texas add Mexico, and in many the introduction of the institution of slavery was added well after it was started in the American colonies. They did not have a religious love of the iconic images of the United States as did New England, they were always looking for the better ways to guarantee self determination and prosperity. A great number of the American population of these states immigrated from South Carolina and Georgia between the 1790s and 1820s where the hatred towards New England was strong, plus a large population of decendents of English Tories from the War of Independence, add that to the ideals and feelings of the "Lone Star Republic" whose roots were deep in the soils of the Mississippi Territory and you have an area ripe to be free from an Union that was not natural to them.