Factories are in cities.
They are manned by civilians.
They are producing ball bearings.
Ball bearings are a major component in military equipment.
Should you bomb the city?
If you do not how do you justify to yourself the loss of the lives of your solders?
The Great Christian Soldiers of 1000 years ago did not seem to get wrapped around the axle like so many self described "Christian moralists" do today. Personally, I view many modern "Christian moralists" as out and out utopian, modernist intellectuals behind a Christian facade. I mean let's face it, saying something like "oh no, ye shall not catapult the castle, there are civilians there" would have been considered sedition, in the day. And you know how they handled such things, in the day ...