That an organization like that only works when the people want to be there and volunteer knowing what they are getting into. That is not the definition of mandatory service.
Plenty of draftees served exceptionally in Vietnam and WWII etc. I think it just takes the right type of motivation. I don't know that I've ever met a Teach for America teacher who had any idea what they were getting into, but a lot of them stick it out.
I had no clue what, in reality, I was signing myself on for when I joined the Army, but I served well.
A sense of duty goes a long way, but that's a larger conversation in America.