Look i get it, Libertarians object to any collectivisms. A Libertarian would see his neighbor's house on fire, and object to paying taxes for the Firefighters to come save the neighbor. Then when his own house is on fire, he would run into the street in a panic, and no one would come help him. I don't want to live in a world like that. I want community and people helping each other. Churches helped facilitate community in the past, but these days, only about 20% of people regularly attend church.
A service obligation doesn't have to mean military, it could be 12 months of community service, there could be options. It's an interesting idea, and of course it will never work in this country, but as a thought experiment I think it could help with many of the trends we are seeing that result in the downfall of nations. The US constitution is our nation and has helped secure our liberties. Collectivism to preserve our constitution and our liberties is necessary.