Mass murder of civilians isn't morally acceptable no matter what the "other side" is doing.
Firebombing a kindergarten in the Rheinland doesn't do anything to help someone in an extermination camp in occupied Poland.
Post war analysis of allied strategic bombing indicates that it did not have a large impact on the war effort and probably wasn't worth the high rate of loss of the expensive airframes and crews.
The bombing didn't cause the German people to overthrow their government like Allied leaders hoped it would, but it did significantly impact the war IMHO by decreasing German production of essential materials like refined oil products, particularly lubricants, ball bearings, airframes and probably other materials.
Even if no factories had been hit, just the fact that the Germans underwent the expense and inefficiencies of distributing manufacturing among many small factories, some underground and some in caves (which the Germans did in fact do) would still have significantly decreased German production.
It can make evaluating things like this tricky. So a raid that lost dozens of bombers and cost weeks in training time only put some part of their industry out of action for a couple weeks and diverted a week or so of other factory productivity for the rebuild and retooling effort—that looks bad, but could still actually be a deal you should take every time under certain circumstances.