It doesn't take a hundred years or access to state secrets to know that involvement in regional power struggles, civil wars, meals-on-wheels, and peacekeeping missions isn't national defense of the US.
Case in point: Bosnia. A blind, deaf, 100 year old could tell our involvement there isn't for our national defense, from day one.
While the majority of US military involvement may have to do with United States interests, those ambiguous and never-defined 'interests' and national defense are seldom the same, no matter how much our government would like us to believe they are.
However, your point does illustrate the importance of selecting more responsible adults as your elected representatives.
I believe the point is that dangerous, foolish individuals will always find a chance to wield the power we mistakenly hand the state. Handing the power of conscription to government is akin to "giving whiskey and car keys to teenage boys". (Credit given to P.J. O'Rourke)
I can't imagine anybody willingly risking their lives to fulfill the political agenda of the quartet you named.
Conscription removes the ability of the people to make that decision. Conscripts will do whatever they are told, or go to jail.
No. That decision is made at the ballot box.
IMHO, conscription is the sole justification for 18-year-old suffrage.
In fact, due to conscription, I advocate full rights, privileges and responsibilities of adulthood for 18-year-olds... voting, drinking, whatever...
Remove the potential for conscription, and I become a staunch advocate of traditional 21-year-old adulthood.
At 18, the teenagers' heads are too full of adolescent mush to be considered adults.