If your cause requires forcing somebody else at gunpoint to comply, it isn't just, it isn't honorable, and it cannot be justified. So, just don't do it.
You, Sir! Yes, you, I say! Would you kindly remove your penis from the screaming lady? No? Well, I shall file a formal complaint with the United Nations of Rainbows and Unicorns, indeed I will!
While war is horrible, atrocious and to be avoided at nearly all costs, sometimes the alternative is even worse. All it takes for evil to triumph is for good men to stand by and doing nothing. And sometimes not doing nothing requires the application of force.