Arguments as soldiers is an alternate label for a conceptual metaphor which is more commonly stated as "Argument is War/Battle". This metaphor is at the core of the adversarial system of debate which is widespread in politics, law and academia.
Politics is the mind-killer. Arguments are soldiers. Once you know which side you’re on, you must support all arguments of that side, and attack all arguments that appear to favor the enemy side; otherwise it’s like stabbing your soldiers in the back. If you abide within that pattern, policy debates will also appear one-sided to you—the costs and drawbacks of your favored policy are enemy soldiers, to be attacked by any means necessary.
Identifying yourself with a side in a political debate may be detrimental to rational evaluation of arguments. Arguments get treated as soldiers, weapons to be used to defend your side of the debate, and to attack the other side. They are no longer instruments of the truth.