Comment by jfengel

Hypothetically, however, if your adversary is indeed without morality, then failing to acknowledge that means working with invalid assumptions. Laboring under a falsehood will not help you. Truth gives you clear eyed access to all of your options.

You may prefer to assume that your opponent is fundamentally virtuous. It's valid to prefer failing under your own values than giving them up in the hopes of winning. Still, you can at least know that is what you are doing, rather than failing and not even knowing why.