Stop clutching yer pearls and moralizing about the fundamentally immoral, when the Russians attacked another country it opened itself up to this shit. If they attacked America, it would be a lot fucking worse and if they used nukes to do it the country would be vaporized. Yes, there are rules in war, and they are routinely violated, especially by the lawless, but you don't stop attacking a vital bridge with civilians crossing it in war, if you have the luxury and tremendous advantage like America does you might be able to show mercy or have another option or wave off capability on a suicide drone. If you punch a stranger in the face, it might be someone who would and can kill you or beat the living shit out of you, this tends to deter such behavior in some people.
Attacking Russian cities is a bad idea for the same reasons it was a bad idea to attack Ukrainian cities, aside from it being a war crime and morally and ethically wrong. It was militarily ineffective, wasted ammo and resources, wore out guns and was bad for your own morale. Now they wish they had that ammo and that their guns work like shit because the barrels are worn out. It was and is stupid and evil, one was motivated by hate and spite, the other would be by retribution, the only justice in war. However, with Russia there are targets that will yield better results than attacking civilians, though civilians would suffer privation because of it. Attacking the transport and power grid at critcal points would work better, however Russian civilians might freeze this winter if the lights went out, so might Europeans and Ukrainians too.