Carrying a Roman soldier's pack for a mile recognises an obligation to the military. Were roles directly supporting the military the only ones offered "in lieu"? Your either/or dichotomy is false. Non-combatant roles that support the military aren't the only options. In most countries, civilian service in lieu can be things like building roads or working in national parks or community service in general. For the most part, no different from working in a country's civil service/public service; a government job.
The WT unnecessarily forced it's loyal followers to become criminals based on its unbiblical false logic.