There's no evidence suggesting that when Confederate General McCausland, under orders from Jubal Early, burned down Chambersburg on July 30, 1864, that his actions were in any way not sanctioned by Confederate high command.
The truth of this matter is that we have a long list of Confederate invasions, raids and guerilla actions in Union states and territories.
Antietam/Sharpsburg & Gettysburg were only the largest of these, but there were many more, and eventually included, without exception, every Union state and territory near the Confederacy, and some quite far removed.
When Confederate forces invaded Union lands, again without exception, they took what they considered legitimate "contraband" (i.e., food, horses), and destroyed what they thought might be of value militarily (i.e., railroads).
Yes, on rare occasion they pretended to "pay for" their seizures, but only with Confederate money, which eventually became worthless.
The burning of Chambersburg, PA -- 2/3 of the city according to this source, $1.6 million in property (circa $300 million in today's values), leaving 2,000 citizens homeless, according to this source -- Chambersburg was their largest destruction of civilian property, but it strongly suggests that Confederates were as fully capable as Union forces of massive destruction, when they believed it necessary.
Therefore, the fact that Confederate destruction of Union lands was not as extensive as Union destruction of Confederate lands simply tells us that Confederates had less ability, and less opportunity to wreck havoc.
So the moral issue here is precisely the same as that of bombing civilian targets during World War Two.
Both sides did it, indeed the enemy started it, but the allied side eventually did more, and it helped them win Unconditional Surrender, and therefore now three generations of peace.
So, are we to condemn allied bombing for the lives it took, while ignoring the much larger numbers who would have died had victory been delayed by months or even years?
The Civil War was more complicated. Yes, the south started things by firing on Ft. Sumter. A measured response would've been a sea blockade or dispatching a marine contingent to retake the fort; not a full scale land invasion of Virginia, which hadn't even joined the CSA until it became clear that they were the main target of the full scale invasion.
Yeah, the burning of Chambersburg was a nasty affair, but it in no way even compared to the scale of what Sherman's army did to Georgia. And, yeah, the ability of the respective armies to visit destruction on enemy territory has some validity unless you consider the relatively benign invasion of Pennsylvania by Lee's army in the month prior to Gettysburg. I will discount the equally relatively benign invasion of Maryland by Lee's army in the month prior to Antietam/Sharpsburg the previous year, given that the entertained hopes of enlisting Maryland into the C.S.A. cause or at least ensuring her neutrality.
They had no such illusions about Pennsylvania in June of 1863. Granted that the war took a far nastier turn post Gettysburg which saw the end of prisoner exchanges, furloughs, etc. But we still have a compare and contrast to what course invading armies took when they HAD the ability to visit massive destruction on the locals: Lee's army in Maryland in August/September of 1862 and Lee's army in Pennsylvania in June of 1863 vs. Sherman's army in Georgia, 1864 and Butler's army in Louisiana and Mississippi in 1862-63.