Neo-Confeds love playing with statistics.
Even if we assume for the sake of argument that there were more abolitionist societies South of the Mason Dixon line (which would, of course, include such places as Maryland, Delaware and DC) the relevant question is what percentage of the Southern population actually belonged to such organizations versus the same percentage in the North.
Since the mere mention of abolition in the south could result in one being beaten to death, since the entire Methodist Church split over the issue, it is safe to say we are dealing with what you appropriatly defined as "Neo-confederates" playing with the statistics.