I think you need to check your timeline. Chambersburg was burnt in July 1864 while Sheridan went through the Shenandoah Valley in September and October of 1864.
Supposedly Chambersburg was burnt in retaliation for the damage done to VMI by General Hunter. I think that the case can be made that VMI was a legitimate military target. It provided hundreds of officers to the confederate military. It would be as if the south had ever made it to West Point and burned it to the ground.
And if burning a town in retaliation is acceptable then if Sherman used Chambersburg as his reason for burning Atlanta then would you find that OK?
Thanks for the comment. I had seen reference on the web (that I can't find at the moment) that Sheridan had given the order and Hunter's troops complied. Doesn't mean that Sheridan himself was in the Shenandoah Valley himself in this particular instance.
Here are some comments by Confederate General Early on why he ordered the destruction of Chambersburg, as reported in Northern newspapers.
General Hunter in his recent raid to Lynchburg, caused wide-spread ruin wherever he passed. I followed him about sixty miles, and language would fail me to describe the terrible desolation which marked his path. Dwelling-houses and other buildings were almost universally burned; fences, implements of husbandry, and everything available for the sustenance of human life, so far as he could do so, were everywhere destroyed. We found many, very many, families of helpless women and children who had been suddenly turned out of doors, and their houses and contents condemned to the flames; and in some cases where they had rescued some extra clothing, the soldiers had torn the garments into narrow strips, and strewn them upon the ground for us to witness when we arrived in pursuit.General Hunter has been much censured by the voice of humanity everywhere, and he richly deserves it all; yet he has caused scarcely one-tenth part of the devastation which has been committed immediately in sight of the headquarters of General Meade and General Grant, in Eastern Virginia. For example--in Culpepper County, where General Meade held his headquarters, almost every house and building has been burned; very few have escaped the flames; and utter desolation is seen on every hand. Even a small tannery in sight of General Meade's headquarters, where a poor man tanned a few hides for the neighbors on the shares, to furnish shoes for the poor women and children who were necessarily left there, was burned by the army, and the half tanned skins drawn from the bats and cut into narrow strips to prevent the possibility of their being useful.
Recently they have burned the house of Andrew Hunter, near Charlestown, with all its contents, requiring his family to stand by and witness the destruction of their homes. They did the same with the house of Edmund J. Lee, near Shepardstown, and repeated it on the buildings of Hon. Alex H. Boteler.
Such things of course, cannot be long endured, and must provoke retaliation whenever it is possible. Accordingly I lately sent General McCausland to Pennsylvania. I did not wish to retaliate in Maryland, because we all hope and believe that Maryland will eventually become a member of the Southern Confederacy. I therefore sent him to Pennsylvania, with written instructions to demand of the authorities of Chambersburg, a sum which would be sufficient to indemnify those gentlemen, and also pay some other damages which I specified in the order; and in default of their compliance, he was instructed to burn the town, which I learn was done. I was very reluctant, and it was a most disagreeable duty, to inflict such damage on these citizens; but I deemed it an imperitive necessity to show the people of the Federal States that was has two sides. I hope and believe it has had, and will have a good effect. I saw with much pleasure, since then, an able article in the National Intelligencer, which called upon the north to consider gravely whether such a mode of warfare as they had inaugurated is likely to yield a success commensurate to its cost.
Looks like I have to add Meade and Grant to the Pillage Honor Roll along with Hunter, Wilde/Wild, Sherman, Butler, and Sheridan. The Federals must have decided if we can't beat them in the field, go after their women and children.