US Civil war, did the average soldier care about slavery?

We need to separate two things here. Why did the South secede and initiate hostilities and the average soldiers motivation. The answer to the former is unequivocally over the issue of slavery. It's been answered so thoroughly over the past few weeks here since that Confederate Flag drama in SC so I'll hold off on that because it doesn't bear repeating.

However while we may not know specifically why every single Confederate soldier fought we do know some statistics about slave ownership. From General Lee's Army: From Victory to Collapse by Joseph Glatthaar, emphasis mine:

Even more revealing was their attachment to slavery. Among the enlistees in 1861, slightly more than one in ten owned slaves personally. This compared favorably to the Confederacy as a whole, in which one in every twenty white persons owned slaves. Yet more than one in every four volunteers that first year lived with parents who were slaveholders. Combining those soldiers who owned slaves with those soldiers who lived with slaveholding family members, the proportion rose to 36 percent. That contrasted starkly with the 24.9 percent, or one in every four households, that owned slaves in the South, based on the 1860 census. Thus, volunteers in 1861 were 42 percent more likely to own slaves themselves or to live with family members who owned slaves than the general population.

The attachment to slavery, though, was even more powerful. One in every ten volunteers in 1861 did not own slaves themselves but lived in households headed by non family members who did. This figure, combined with the 36 percent who owned or whose family members owned slaves, indicated that almost one of every two 1861 recruits lived with slaveholders. Nor did the direct exposure stop there. Untold numbers of enlistees rented land from, sold crops to, or worked for slaveholders. In the final tabulation, the vast majority of the volunteers of 1861 had a direct connection to slavery. For slaveholder and nonslaveholder alike, slavery lay at the heart of the Confederate nation. The fact that their paper notes frequently depicted scenes of slaves demonstrated the institution's central role and symbolic value to the Confederacy.

More than half the officers in 1861 owned slaves, and none of them lived with family members who were slaveholders. Their substantial median combined wealth ($5,600) and average combined wealth ($8,979) mirrored that high proportion of slave ownership. By comparison, only one in twelve enlisted men owned slaves, but when those who lived with family slave owners were included, the ratio exceeded one in three. That was 40 percent above the tally for all households in the Old South. With the inclusion of those who resided in nonfamily slaveholding households, the direct exposure to bondage among enlisted personnel was four of every nine.

It's a very important fact that is often overlooked: You don't need to be a slaveholder to have an ideological or economic stake in slavery. Those who had family who were slave owners, lived or worked on plantations in other regards that relied on slave populations, or those who did totally other jobs in regions whose economies were supported by slaves. All of them would be in jeopardy with slavery disappearing. Look at the personal motivations beyond all that for self-preservation. In many Southern counties and cities slaves were a massive population, often greater than the white population. Free blacks with voting and legal rights instantly shifts balance of power everywhere but especially in those regions. With a thoroughly racist population to say the least many would not look favorably upon that.