What would that make conscious objectors? Unqualified for Citizenship? That's not going to fly over, considering the many religious groups that left England and, or where banished to America and, in being loyal to their religious orders as American were excused from military duty in the campaigns against the Natives, and later in the Revolutionary War and every war after to include the recent conflicts in Afghanistan and Iraq.
Many of the founders and original authors and signers of the Declaration or Independence, and Constitution came from those long established religious orders and opened America's first universities and schools.
How do you exclude their descendants from Citizenship?
There is a lot about America you know nothing about.
The overwhelming majority of citizens haven't earned their citizenship; it was given to them (myself included) just for being lucky enough to be born on US soil. A small percentage of us have subsequently earned our citizenship through military service.
We will encourage our daughter to join the military after she graduates high school, but we obviously can't force her to do so. She already knows she is on her own financially after age 18, so any college or vocational training will entirely up to her. She has already started her own investments which she gains control of when she turns 18.
I'm contending the US would be much better off if citizenship were earned.