^^
He would have to fight whether he liked it or not. And yes, serving in the reserves, and fighting a war are entirely different.
Personally I would never join, and dont find any wrong in joining, but I think they are making a huge mistake by targeting "JOIN THE ARMY" to young highschool/college students.
My brother did a term in the Army, and is now a sgt. in the Marines. He is currently fighting in Fallujah.