The claim does not stand because it places a great deal of weight on a thin reed. In truth, secession would not have been undertaken if it was thought likely to lead to the end of slavery.
Of course it stands up. What does not stand up is that 94+% of White Southerners voted to secede in order to protect the property of 6% who owned slaves....even though slavery was not threatened in the US and even though the union government went miles out of its way to make it clear that slavery was not threatened within the US.
What makes much more sense is they felt they were being screwed economically and wanted out.