The Field Manual states that "Abuse of detained personas is immoral, illegal, and unprofessional. . . Torture and cruel, inhuman, and degrading treatment is never a morally permissible option, even if lives depend on gaining information. . ."
In addition to morality and legality, the Field Manual also provides another reason that for opposing torture and abused of suspected insurgents. It is the historical example of the use of torture during the Algerian war of independence by the French military. I think the title of this section says it all, "Lose Moral Legitimacy, Lose the War". The "failure to comply with moral and legal restrictions severely undermined French efforts and contributed to their loss despite several significant military victories." The use of torture undermined the French governments moral authority and "empowered the moral legitimacy of the opposition". Finally the use of torture "degraded the ethical climate throughout the French Army.
Lose moral legitimacy, lose the war. I would think that doing what is moral should be justification in itself but for those who do not think this is a sufficient reason not to torture the Army Field Manual provides another reason. We will lose the war. Perhaps when you consider all the moral stains to our country's honor that have occurred under the Bush administration (Abu Ghraib, Haditha, Black Water, etc.) maybe the war has long been lost. Our betrayal of our values makes us weaker instead of stronger. So why does President Bush want to veto these restrictions on "enhanced interrogation" techniques?