Civil War historian here. Coincidentally, I also grew up across the street from Lee’s headquarters at Gettysburg.

In the case of the Civil War, it’d be hard to say how many soldiers shot to miss vs shot to harm because there were no studies that systematically interviewed them about this issue. There are anecdotal examples of soldiers talking about picking targets, like Samuel Watkins of Tennessee who said he never shot at officers because the enlisted men were more of a threat.

Earl Hess’s “The Rifle Musket in Civil War Combat” might help you out. He argues that the rifle musket was so deadly during the war because soldiers preferred firing at short range, had gotten very good at killing soldiers via sniping and the skirmish line, and the parabolic trajectory of the rifle musket’s bullet (which created two kill zones instead of one).

This would suggest that most front-line Civil War soldiers were very willing to shoot to harm; however, panic, smoke, fatigue, and other battlefield impediments may have limited their ability to hit targets. This was the case at Gettysburg, where soldiers panicked and double, triple, and quadruple loaded their muskets.

My research suggests instances of deliberately missing a target were rare during Civil War combat. If a soldier wanted to avoid killing, there were other ways to do so. James McPherson writes about incidents of skulking in “For Cause and Comrades.”

Hope this helps.

There's always more to be said on this topic, but you might be interested in this previous answer which discusses the accuracy of firearms during the early modern period. The idea that most soldiers during this period fired into the intentionally in order to avoid killing anyone doesn't seem to be very widely accepted. The accuracy of muzzleloading firearms did tend to drop dramatically when soldiers were on the battlefield, but typically explanations for this then and now tend to focus more on fear, adrenaline, noise, smoke, etc.