"With these truths in mind, this most holy synod makes its own the condemnations of total war already pronounced by recent popes,[2] and issues the following declaration.
"Any act of war aimed indiscriminately at the destruction of entire cities of extensive areas along with their population is a crime against God and man himself. It merits unequivocal and unhesitating condemnation. "
This quote is from a document called "The Pastoral Constitution on the Church in the Modern World." It comes from the last (Catholic) Ecumenical Council and has the form of a teaching which is solemn and universal.
I quote it here, not because I think you have any particular ties to the Catholic Church (I don't even know you) but because anyone with any ties to "God" or "man himself" ought to seriously consider the moral evaluation of an act which indiscriminately kills noncombatants.
There are very few acts that can't ever be justified by context, pretext or precedent. The deliberate taking of an innocent life is one.
It doesn't matter whether something similar or 1000 times worse was done to you beforehand. It doesn't matter whether it's done by abortion, a bomb, or a baseball bat. It doesn't matter whether you think it'll have good consequences. It doesn't matter whether it's soon covered over with rubble or flowers or a brand-spanking-new city, democracy, free enterprise, and peace.
It's still putting your crosshairs on the innocent and pulling the trigger. It's still murder.
Hard to argue with an objective fact, but I'm sure some will try.
Intentionally targeting civilian non combatants is wrong. War is never "good" but can be just. WWII in the end was a just war because if Germany hadn't been stopped, there is no telling just what would have happened.
The better question is would WWII happened if we (the US) stayed out of WWI?
"The deliberate taking of an innocent life is one. "
Even so-called "collateral damage"?
Not if it prevents far more murders. In such a case, refusing to pull the trigger is murder.