If you don’t believe in the mission, you won’t do what’s necessary to achieve it.
Leaders must believe in the mission. In order to believe in the mission they must understand the mission. Asking why is not a sign of weakness nor disloyalty. It’s your duty to ask why until you understand the mission, or until you’re able to push the mission to something you can understand. Otherwise it’s probably not your mission. You won’t make the necessary sacrifices and take the necessary risks.