Treason against your country is considered the highest of crimes. It is a capital crime, punishable by death, and can be sentenced by a court martial and sentenced without appeal or trial by jury. The label of traitor is among the most offensive that can be applied to a citizen.
To be willing to commit treason is to reject the idea of loyalty to one’s nation in favor of another loyalty, whether loyalty to self-advancement or loyalty to some ideal by which the actions of the nation can be judged.
Now imagine this scenario: You are a citizen of a nation at war. You believe in the war, in your leaders and in the rightness of your cause. As the war drags on, a deadly disease strikes first your troops, and then your citizens. As a matter of national security, this disease is quarantined and kept top secret, and most of the population is unaware of its existence. Still, it spreads easily, and kills at a prodigious rate: a full 2/3 of those infected die (as compared to the 1/3 mortality rate of the Black death), and of those who survive, there is no real recovery: they simply remain ill indefinitely.
Fortunately, an unlikely discovery yields an unexpected cure. Soon, the disease is stamped out among your nation’s soldiers and citizens, though now your nation is at an overwhelming disadvantage against your enemy, whose troops have not been touched by the disease.
Until you learn that your national leaders have deliberately planted the disease among your enemy’s major cities and military bases. The disease has not been quarantined (as it was in your nation), and is rapidly spreading beyond your enemy’s borders. Soon, instead of being the weakest military in the world, your nation will have the strongest military. As such, the nature of the cure is a top national secret, known only to a handful of people. You are one of those people.