1) Approach ignorant, liberal person talking about peace and saying there should be "no retaliation"
2) Have a brief conversation with them and ask if military force is appropriate.
3) When he says, "No." ask him, "Why not?"
4) When he says, "Because that would just cause more innocent deaths, which would be awful, and we should not cause more violence."
5) Punch him in the face . . . hard.
6) When he gets up to punch you, point out to him that it would be a mistake (and contrary to his values) to punch you because he would be causing more violence.
7) When he agrees with you that he has pledged not to commit violence, punch him in the face again . . . only harder this time.
8) Repeat steps 2 through 7 until he understands that sometimes it is necessary to punch back.
You left out "Kick him while he's down" between numbers 5 and 6 ;-)