Stalin had been criticising the Allied Leaders - Churchill in particular - about the lack of a "second front" and refused to accept the bombing campaign as the only alternative. At Yalta, Stalin asked for bomber attacks against reinforcement centres and this gave Churchill the opportunity to show what Bomber Command had been achieving by attacking a target on the Soviet line of advance. It would also demonstrate to Stalin the power of Bomber Command should Stalin decide to continue on after Berlin. Perhaps this is why such a large bomber force was sent to attack this target (perhaps larger than necessary?) and the subsequent firestorm which was a rare event during WW2 (there were only about 6 produced throughout the war?).
However, War Crime Trials against the German leaders was also publicised at Yalta, and after Dresden the German leadership countered this by openly releasing uncensored footage of the raid, for the first time in the war, together with hugely inflated casualty figures of 400,000. This propaganda was picked up by the usual suspects in the House of Lords who personally attacked Churchill just as he was facing a general Election in a few months time. The result was that Churchill side-stepped to let Bomber Command carry full responsibility.
Churchill thought that Dresden (and the other 3 raids at this time) would give him some degree of morale justification to Stalin but sadly it rebounded leading him to betray those very people who had given so much to the overall war effort.