Both sides bombed civilian targets. It's pretty hard to defend what the Allies did to Dresden: firebombing a target devoid of military significance (but full of women, children, elderly men, refugees and POWs) as a retaliation. Not content with the devastation caused by the fire-bombing, the Allies sent in more planes the following day to strafe survivors who had escaped the inferno and made it out into open areas.
Personally, I find it impossible to defend this action. I've seen pictures. The one that sticks in my mind was a photograph of a corner of building that was mostly incinerated, with a chalk message scrawled on it saying "Mutti wir suchen Dich" (Mummy, we're looking for you). Such messages scrawled on buildings and ruins were seen all over Dresden after the inferno. I know someone who was a 10-year-old child in a suburb of Dresden when it was fire-bombed. Her school was turned into a makeshift first aid station for victims.
This is not to imply that I'm defending the Nazis. Believe me, I am not. But as far as I can recall, the first German bombing that hit civilian targets was accidental and actually pissed off German leadership, who still thought that they might be able to come to an agreement with the Brits so that they could then loose their full fury on the unlucky Slavs.