I know the Genevea convention didn't exist at the time, and that people muscharacterize what "collective punishment" even is frequently.

I don't understand history or law enough to know if this would be considered collective punishment... does anyone know?

Sherman knew what had to be done to cut out the rot. Unfortunately, other US leaders didn't.

Even Sherman called it "hard war." This site goes into the history pretty deeply, although I can't speak for bias, which I expect with its name:

https://billofrightsinstitute.org/essays/william-tecumseh-sherman-and-total-war/

The gist I pick up from reading this is basically, the viewpoint was that if you were a civilian in the south not resisting, than you were abetting. You weren't considered a adversary, but your goods were forfeit and they would not take care to ensure your safety. It was done specifically as psychological warfare, to show the confederates that the war could effect them.

Not really, while Sherman is characterizing it with collective guilt, the punishment is that the city's fortifications were bombarded until it surrendered.

Thing is, that resulted in a lot of... collateral damage, even though civilians were not targeted.

Yeah, it certainly wildly predates anything even remotely qualifying as a "precision munition". I'm curious how the concept "reasonable collateral damage" was shaped (if at all) by the availability of more discriminate munitions.

I hear you. I guess from a practical standpoint... how would anyone know which civilians were helping or retarding the confederate war effort and by how much? It's a spectrum, right?