Put yourself in the shoes of the Allied war-planners in the months leading up to Dresden. In Jan '45, US Army Air Forces have just told you they've lost the initiative and that the Luftwaffe have recovered to a degree thought impossible. Also in January, a Joint Intelligence subcommittee tells you that the probable worst-case scenario had the Germans stopping the Allies dead in their tracks until Aug given the balance of power at the time. It would be reasonable to be concerned and wish to keep hitting Germany hard so they couldn't hit too hard back.

Also the US had suffered just under 50 000 casualties in January 1945 alone. The war was winding down but the Allies didn't know that, or at least couldn't behave as if winning was inevitable. On top of military casualties, how many were dying in concentration camps? The war wasn't winding down for them.

The actual bombing of Dresden wasn't perfect. Lots of strategic targets were missed and city centres or populated areas hit instead. However, the idea of bombing Dresden, in of itself, wasn't flawed.