Not really. Your statement doesn't account for the 90% of people who didn't own a slave in some States, and their motivation in voting secession.
It's not that they thought they would gain under the slave system. The economic pressure, after all, was there. It's why Southern whites came to hate black slaves and freedmen, because of the planters' constant competitive threat to confound the yeomanry with bondmen of a conquered and prostrate race. That was the real significance of the racialization of slavery: it alienated freemen and slaves, and it marked the black race in the eyes of white working men who were trying to stay above water. They didn't want to end up like the slaves, and they resented it every time they worked elbow to elbow with slaves in any setting. (Thus T. R. Fehrenbach's explanation of some of the social stresses introduced by the planters' reliance on chattel African slavery.)
Rather than gain from the slave-labor system, whites looked more to secession to preserve what they had from the hostility of sectional bigots in the North, esp. among the literate classes who were the supporters of John Brown, and who actively and openly wanted to see a race war submerge the white South in blood, flames, and universal slaughter, just like Haiti. Fehrenbach points out that Northerners seem never to have gotten this point -- that just the threat of a race war was absolutely a declaration of war on the whole society: it caused people to turn violent instantly, and it brought to life, like a chemistry-lab demonstration of violent flammability, the 103-year spectacle of Southern lynch-law, hitherto unheard-of. (It was lost on Southern audiences, in their state of extreme survival-time excitation, that Abraham Lincoln deplored Brown's raid and what it stood for as much as Col. Robert E. Lee did.)
I'd suppose that many of your 90% who didn't own slaves either didn't vote, being women or children or slaves themselves or voted against secession.
In a state like Mississippi or South Carolina, where something like half the population had a slaveowner somewhere in the family, the vote for secession was higher than in states where slaves and slaveowners were rarer.
You are right that for many people it was more a matter of fear than of opportunity. But we were talking about elites, about people who owned many slaves and those who aspired to own slaves.
Further down the social ladder thinking was different and there was that fear of being submerged in the slave population or destroyed by rioting slaves or ex-slaves.
Rather than gain from the slave-labor system, whites looked more to secession to preserve what they had from the hostility of sectional bigots in the North, esp. among the literate classes who were the supporters of John Brown, and who actively and openly wanted to see a race war submerge the white South in blood, flames, and universal slaughter, just like Haiti. Fehrenbach points out that Northerners seem never to have gotten this point -- that just the threat of a race war was absolutely a declaration of war on the whole society: it caused people to turn violent instantly, and it brought to life, like a chemistry-lab demonstration of violent flammability, the 103-year spectacle of Southern lynch-law, hitherto unheard-of.
In the first sentence the Northerners "actively and openly want" a "race war," and in the long second sentence you say they just never got the point. Few people in the North wanted any sort of "race war." Some just wanted what they saw as liberty and justice. And Southerners reacted to what they saw as the probable consequences of emancipation.
While lynching certainly was characteristic of the post-Civil War South, I don't think you can quite argue that such mob violence was "unheard-of" before the Civil War. But it wasn't a racial phenomenon before the war in the way that it was afterwards.