Current events have brought the concept of “proportionality in war” to the lips of journalists and analysts. Often they seem not to know what it has meant. In “just war theory,” the requirement for “proportionate means” is not a synonym for “equivalent damage or casualties.” It simply means using means proportionate to the just end you are seeking.
If an aggressor fires on you, stopping the aggression may require military means that inflict significantly more casualties than those you sustain.
I can do no better than quoting the same 20th century ethicist, Paul Ramsey, quoted by Keith Pavlischek at The New Atlantis a decade ago when conflict between Israelis and Palestinians occasioned this same debate.
One does not calculate a prudent number of babies to be murdered (directly killed) for the sake of any good consequences (such as getting at the government); but one may and must calculate the prudent number that will and may be killed as an unavoidable side or collateral effect of military operations targeted upon the force to be repelled and whose goal and other consequence is expected to be the saving of many more from slaughter or from an oppressive tyranny, or in order to preserve in the international system accepted patterns in the actions of states on which grave consequences depend. Direct attacks on a civil population can never be justified; but unfortunately — in this world to date — a good many incidental deaths and extensive collateral damage to civil society may still be knowingly done lest worse befall.