The fire bombing of Dresden was highly controversial, yes. By that point in the war, most of Germany's war industry and the bulk of what was left of the Wehrmacht, Luftwaffe, and Kriegsmarine had been destroyed. And yet, they were still fighting tooth and nail for every inch of ground. War casualties by late 44' and 1945 were catastrophically high as Germany had suffered enormous losses on both the Eastern and Western fronts. Old men and young boys were being conscripted and needlessly killed by allied armies, and the Axis had successfully switched their propaganda from it being a war of conquest to a war of survival. On top of that, you also had an incredible amount of civilian displacement occurring as the German armies collapsed, and the people feared retribution. One of the untold horrors that occurred was the loss of life that happened after the war ended as a result of these mass migrations.
And so you had these controversial actions happen like Dresden where it was partly an Allied attempt to end the war. "Just f'ing give up already!", the Allies would say, as the Axis Armies would just not quit. The culmination of these types of acts were the atomic bombs. It does not justify acts like Dresden, no, but you have to understand the unimaginable carnage witnessed by this generation, who were all so desperate to end the war.
The Second War World truly was the most destructive, wasteful, and horrific wars of modern history. That is the legacy of the Nazi regime.