I completely agree with you that mandatory enlistment is essentially never acceptable as if a conflict is so dire, you'd expect citizens to feel empowered to join the fight without fear of penalty or retribution if they didn't.

That being said, I think most of what you were replying to was not an argument for mandatory enlistment, they were suggesting that we might want to include a couple years of work placements following high school, with one option being military service but other choices being available and none decided by the government. I also believe they were suggesting that the penalty for not doing so would be similar to penalties for not attending high school and not what we've seen countries implement as penalties for conscription. I'm not saying that plan is perfect but I can at least see a significant nuance between their suggestion and military conscription.