The problem with Jens argument is that it doesn't address the issues at the time. Assuming he/she agrees that ending the hold of the NAZI party on Germany and Europe was a desirable and necessary thing how was it to be achieved?
The answer was an alliance of many nations, none of whom could be described as without some serious faults themselves but nothing like as mad, bad and dangerous as Hitlerian Germany. Once you start a war you unleash death and destruction - this is why it should be avoided if at all possible - but by 1939 there really was no choice - it was literally fight or be subjugated. You fight to win, and to win as fast as possible - no one seriously holds the view that Hitler winning would be a good thing for anyone, especially Germany. For many years the Allies in the West had a very limited options on how to fight - the bombing campaign was the main answer. We should also remember that it wasn't started by the Allies - Germany was quite happy to bomb anyone.
We can say it was awful, we can say it would have been better if we could have won the war without doing it - but we can't say it was wrong at the time or that the people who carried it out weren't very brave. It's like any other battle - thousands killed and wounded and awful destruction but there really is no choice - sometimes it's necessary.