I like that quote.  The heart of it is the word "enemy" - it means you have to separate those who are enemies from those who are just disagreeing on the means but not the ends. 

You give no aid to the enemy because they don't have the same end in mind.  With those who disagree honestly about how to get to a shared end, you are benefited by explanations and debates.  But this depends upon honesty.  Some enemies lie and pretend they share the same end when they don't.  Progressivism, especially since Saul Alinsky, treats lies as justified by their ends - just as Jihadism explicitly tells its adherents to lie about their ends (both the peaceful infiltration encouraged by the Muslim Brotherhood, and those planning violent Jihad acts of terrorist).

So, the idea is don't justify, or in effect, sanction enemies with explanations and debates as if they shared common ends when they don't.  It does require understanding who is an enemy.  Those who make lying an accepting practice automatically makes themselves an enemy (progressives and Jihadies for example).