The Zimmerman telegram could be described as the key leading to an allied victory and the end of the war. However, after being deciphered, Admiral William Hall decided to keep America in the dark, withholding the contents of the telegram from President Wilson. Despite the immediate danger this posed to the United States, I believe Admiral Hall made the correct decision. Disclosing the contents of the telegram would have alerted the Germans to the vulnerabilities in their encryption, leading them to create more secure ciphers and eventually cutting off British access to German information.
Essentially, this boils down to whether or not "the end justifies the means". Although this paved the way to an allied victory, keeping the telegram a secret endangered countless american lives. One could argue Admiral Hall's decision was extremely unethical, as it unnecessary risked peoples' lives. Needless deaths must be avoided, even if it leads to a faster victory. The means are simply too cruel to justify the end. However, keeping the telegram a secret potentially changed the course of the war. Although American involvement was believed to ensure an allied victory, it was not guaranteed. The British access to German intelligence proved to be invaluable to their war effort, and saving more lives was not as important as keeping these intelligence lines open. With this intelligence, the British forces could always stay one step ahead of the German offensive. This aided greatly in preventing the Germans from dominating the war, and essentially allowed the allied forces to emerge victory. Thus, safekeeping this crucial line of intel proved much more important than saving more american lives. In addition, Admiral Hall's plans to intercept the German's telegram in Mexico would lead to President Wilson learning of the contents of the Zimmerman telegram. Although he would learn of its contents late, the effect of the telegram still stirred America to action. Thus, immediately sending the Zimmerman telegram to America was not even completely necessary. Overall, victory was the main objective, and thus the end did justify the means.