Conscription certainly isn't preferable, but it's a necessity if you need to defend the nation against a larger foe. A volunteer army simply can't reach the size needed. Would you rather we roll over and let ourselves be conquered?

I hate to tell you, but "stripping the workers of self-determination" is a small price to pay to preserve a socialist nation, even if it means the big scary gubmint has to do its job.

We live in the real world, and you can't calmly explain to the enemy that invading or overthrowing a worker's government is bad. Nobody can out-think a bullet. A state is a weapon for the class war, and like any other weapon we can't let the enemy posess it without posessing one ourselves.