I think it should be up to local school boards.
I don't understand the doctrinaire opposition to this. It's hardly indentured servitude, it's beneficial to both the students and the community, and it even helps with college admissions. It's not as if anyone wants the students to be required to smash rocks in the hot sun 80 hours per week.
The collectivists operate by incrementalism. When the income tax was started the top rate was only 7%, and very few people had to pay income tax at all. But in 31 years the top rate had risen to 94%. Today the top rate is less than that but virtually everyone pays income tax. The lowest bracket is now 10%.
Social Security was started in the 30's. Then in the 60's Medicare and Medicaid were added and recently Bush added prescription drugs. Medicare and Medicaid now cost 100 times as much as they did when they were started.
My point is that once you allow government to require service from the people, there is no limit to how far they can take it. That is a great danger. Once the precedent is set the number of people who must provide service can be expanded and the hours they must serve can be increased to whatever limit the bureaucrats want. Also since service is a government requirement there will be penalties for not complying. The penalty for students who don't comply is harsh; you don't graduate. What might it be for adults who don't comply?
You make good points and I am distrustful of increased governmental power. Still, I think this is a small matter.
Also, some power has flowed away from the government. The military draft was a staple of American life for over 3 decades, until the mid 1970s. When the draft was ended, it was assumed that it would be reactivated if there was ever a war. But we've had three wars, and no draft.