[The following factual information relies heavily on Wikipedia. Its interpretation and emphasis is my own.]
The military rationales for destroying the city were
Every reference in this list of rationalizations to preventing troop movements through Dresden is a self-serving lie. First, railroads do not route all their tracks through population centers and second, it has been known by military planners at least since World War I that the repair of railroad trackage, as distinct from large railroad terminals, is easily and quickly done.
The real question is, why were they lying?
The firebombing consisted of by-then standard methods; dropping large amounts of high-explosive to blow off the roofs to expose the timbers within buildings, followed by incendiary devices (fire-sticks) to ignite them and then more high-explosives to hamper the efforts of the fire services. This eventually created a self-sustaining firestorm with temperatures peaking at over 1500°C (2700°F). After the area caught fire, the air above the bombed area became extremely hot and rose rapidly. Cold air then rushed in at ground level from the outside and people were sucked into the fire. US fighter aircraft strafed the evacuation routes to add to the chaos.
But it was not the intent of Bomber Command to kill civilians.
Out of 28,410 houses in the inner city of Dresden, 24,866 were destroyed. An area of 15 square kilometers was totally destroyed, among that: 14,000 homes, 72 schools, 22 hospitals, 18 churches, 5 theatres, 50 bank and insurance companies, 31 department stores, 31 large hotels, 62 administration buildings as well as factories such as the Ihagee camera works. In total there were 222,000 apartments in the city. 75,000 of them were totally destroyed, 11,000 severely damaged, 7,000 damaged, 81,000 slightly damaged. The city was around 300 square kilometers in area in those days.
But it was not the intent of Bomber Command to kill civilians.
The number of civilians killed is not known. Official estimates range from 25 to 35 thousand to as high as 300 thousand.
Trains caught in the railway station in the raid were found to contain refugees from the eastern front.
Although the main railway station was destroyed completely, the railway was working again within a few days.
The cavalier defenders of Western Values and advocates of the preciousness of human life undoubtedly would argue that those few days made it all worthwhile.