What other options were there for the Allies?
By 1943 the Germans had mostly successfully moved their production to small workshops, which were often in cities. This is also in the long shadow the Blitz cast, which inflicted not dissimilar damage to London.
If London was a valid Military Target in 1940, then Hamburg was certainly one in 1943.
To quote from wikipedia about sessions learned by the British the Blitz "From 1943 to the end of the war, he [Harris] and other proponents of the area offensive represented it [the bomber offensive] less as an attack on morale than as an assault on the housing, utilities, communications, and other services that supported the war production effort."
They do get one thing correct however - the horrors of the Nuclear Bomb are not that unique, many many more were killed, in Europe and Pacific theaters by firebombing (I'll point folks at the firebombing of Tokyo as a starting point) as the than were killed by nuclear bombs.
Both Germany and Japan violated the normal, commonly understood rules of war - we responded, in ways that, could be argued to have an ethical shadow - and while I dont consider these acts unethical (including the nuclear bomb), they're not ethically clean - they're a gray area that can only be justified in context.
We have this mental narrative of war that its this clean thing, either black or white, just or unjust - and thats not reality, war it dirty, even when its just and good - for a good reason, it means much death and killing, it leaves indelible stains on those who fight, and those who survive for the rest of their lives. To present otherwise is foolish and lying to ourselves.