Sure; and there were massive civilian casualties in WWII. If WWII could be prevented at the cost of e.g. entirely obliterating Berlin in 1935, it would be "worth it", strictly as a matter of lives lost and saved. Would it prevent WWII? That's a valid subject for debate, and the debate would have gone differently in 1935 than now with the benefit of hindsight. Ditto for 1946.
The prevailing military doctrine at the time was ‘total war’, and it was implemented with strategic bombing campaigns. The weapons were so inaccurate that they simply kept dropping bombs until everything was destroyed.
Any war on the Soviet Union, either nuclear or with conventional firebombing would have caused massive civilian casualties.