It was the very real threat of the Northern Abolishionist, supported by the fear of the Lincoln Government was supporting them, to instigate a slave revolt within the Southern States. This is signaled by the timely surge of local Militias companies throughtout the southern immediately following after John Browns Harpers Ferry raid. A raid which avowed purpose was to do just that, arm the slaves for such a revolt.
This is also supported by the number of new laws passed to control freemen of color in the southern states. The fear of a slave revolt started by the abolishionist and supported by the Northern states and the Federal Government was the factor that drove the south to feel the need for secession. The impact of John Brown's Harpers Ferry raid was no small event to the charging of the South attitudes for the need to protect themselves and take matter into their own hands and not depend on the Nation Government for a solution.
It did not take a "fire-eater" for the southern people to see the threat plainly and the rise of the militia was in fact to maintain civil order in the case of a slave revolt.