At sea, instead of the customary practice of tethering their mines and then declaring an area mined, the Germsans decided it would be a good idea to mine the home waters and not tell them, and then, to add insult to injury, not bother to tether their mines. All in flagrant disregard to treaty obligations they had willingly signed up to
Well before the British started to get nasty, the Germans were already investing heavily in terrror bombing and other questionable practices. It beggars belief to think the British would sit around forever and fight the war with handicaps like observing the rules of war for bombing, when clearly their opponents thought nothing of ignoring the accepted rules of war.
It really depends on what the goals are ... and my bigger arguments against terror bombing (or use of terror in general) is not on moral grounds or even ethical ones (though there's plenty there), but actual strategic and tactical efficacy both in the short term and long term. (ie in terms of fostering post-war stability)
If the goal is to destroy the enemy without any concern for the long term consequences, then sure ... the 'total war' strategy makes sense. If you actually care about avoiding the propagation of further (potentially worse) conflict, then far more calculated and precise planning is necessary. (like actually avoiding the cold war ... and avoiding repeating the mistakes of WWI) Though even there, I'm not certain that terror bombing was particularly useful (by any side) compared to resources being alternatively focused.
There's also the ethical issue of minimizing harm in general, destruction of life, culture, and history (art, literature, architecture, etc -obviously some of which the Nazi book burnings had destroyed, though others saved by plunder and hoarding of works that likely would have been otherwise destroyed). Those issues obviously become even more difficult once scorched earth tactics are being employed by the enemy as well, complicating invasion plans if the goal is capture without massive destruction of architecture/infrastructure and technology (let alone the more ethically motivated art/etc).
And of course pragmatic compromises to all of that, but rather few of the more destructive strategies and tactics used in WWII were particularly pragmatic, not that Britain was the worst offender there by any stretch. (Germany never regained counsel or leadership on the level of Bismark, and America didn't have leadership on par with Teddy Roosevelt -who'd certainly have been amazing to see in officer for either of the World Wars ... that is if there'd even been a second had he been in office during the first, and Churchill does indeed seem to have been one of the commanders of WWII to genuinely come closer to that level)
Churchill certainly seemed to see a great many more of the post-war problems than did his contemporaries, particularly relating to Stalin and Soviet expansion and solidification of power. Of course, ending the war in Europe earlier by allowing more conditional terms of surrender on the Western Front alone would certainly fit more into the pragmatic category on top of plenty of other motives making it appealing to the Western Allies as well as Germany.