To drill down on this a bit, by "the sword" do you mean "all violent human acts"? I'll be open with my position, which is that I do not believe that the New Testament categorically rules out all forms of violence/coercion for Christians. It might be interesting for us to examine where exactly we differ in our interpretation of various passages.
Do you derive this belief from the New Testament? If so, where do you find the exceptions?
The principle of double effect is not saying that two wrongs make a right. It rather states that one may morally do something (an action) that has two effects, one good and one evil, provided that certain conditions are fulfilled. I think that most people will admit such a principle in some form - though the details of the conditions do matter.
Here is one example. Suicide is wrong, but if a vicious tiger is charging towards a child who is running away and almost at the door of a house, a mother may without moral blame place herself between the tiger and the child. She does not will her own death as a result of this action (she would much rather not die), and if she happened to not die as a result, there would otherwise be nothing blameworthy about her action. The good effect (the saving of the child's life) is also produced directly by the action she takes. It is also a grave or serious matter - she should not carry out such an action for the sake of, say, a pet fish. In the end, many people would agree that her action is morally good even though it has an "evil" effect - namely her own death or at least serious bodily harm.
Another example which I hesitate to bring up on this forum because I've seen some of the heated discussion about it (
) is vaccines. Again, people disagree here. But if you do decide to take a vaccine that is "abortion-derived," then in a sense you (and possibly those around you) are benefiting from an evil act. So the question becomes: are there certain conditions under which it might be permissible to benefit from a grave evil act? A variant of the principle of double effect can be used to argue that in the specific case of the covid vaccines, taking the vaccine can indeed be a morally justifiable act. (You might or might not agree in this particular case, and my intent is not to sidetrack this into a vaccine argument.)Some more examples relevant to the current discussion where the principle of double effect might be applied: paying taxes that are then used for evil actions, living in a town where order is kept by a police force using what you believe to be evil/wrong actions, buying groceries from a store that endorses and promotes evil, buying a book from a company that prints other books aimed at corrupting children, driving on a road that was built due to bribes paid to a corrupt politician, etc. I am confident in saying that at some point in your personal moral choices, you do indeed apply some form of the principle of double effect. Or to put it another way, you in some way benefit from evil even though there is the possibility of making a choice that would remove that benefit. Again, different people draw the lines here in different places regarding what is justifiable and what isn't - I'm just emphasizing that everyone applies the principle in some form or another and indeed cannot avoid doing so.