What to do if you happen upon a peace rally by a naive hemp-shirt-wearing hippie, to teach them why force is sometimes needed:
1) Approach dumb ignorant hippie talking about "peace" and saying there should be, "no retaliation."
2) Engage in brief conversation, ask if military force is appropriate.
3) When he says "No," ask, "Why not?"
4) Wait until he says something to the effect of, "Because that would just cause more innocent deaths, which would be awful and we should not cause more violence."
5) When he's in mid sentence, punch him in the face as hard as you can.
6) When he gets back up to up to punch you, point out that it would be a mistake and contrary to his values to strike you, because that would, "be awful and he should not cause more violence."
7) Wait until he agrees that he has pledged not to commit additional violence.
8) Punch him in the face again, harder this time.
Repeat steps 5 through 8 until they understand that when push comes to shove, it is necessary to punch back.
These steps work just as well on female versions of naive hemp-shirt-wearing hippies.