What to say to students?

What to say to students when they don’t want to write the argument for the side they disagree with?

Maybe this will work.

Sun Tzu, the Art of War:
It is said that if you know your enemies and know yourself, you will not be imperiled in a hundred battles; if you do not know your enemies but do know yourself, you will win one and lose one; if you do not know your enemies nor yourself, you will be imperiled in every single battle.