That's reason they are allowed to use it, and we aren't is Rule #4, "Make the enemy live up to his own books of rules."
In other words, "we must hold ourselves to a higher standard" than the Alinskyites, so they can mop the floors with us.
The best standard we can hold ourselves to is remember that the Alinskyites are like spawns of the devil (remember Saul Alinsky’s dedication in “Rules for Radicals?). If we keep this in mind, while keeping a good sense of humor at the same time, we will do okay. We should not let people who simply fight dirty lay a guilt trip on us.