1.) Approach student 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.
6.) When he gets back 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.
9.) Repeat steps 5 through 8 until he understands that sometimes it's necessary to punch back.