When I was young, I did a lot of things I now deeply regret. Your brother will feel that what he is doing is important for the nation and an affirmation of his manhood. Trying to talk him out of it will not work and be very hurtful to your family. Just let him know you will always be there for him, because someday he will need you. Because just as sure as God made little green apples, she will have us in another bullshit war just as soon as she can.