As an anarchist, this is one of those things like freedom of movement and settlement (aka uncontrolled immigration) where I believe separating between current reality and hoped future is fundamental.
To begin with, Germany is not a liberal utopia. It's a Corporatist regime, like the rest of the developed world. To follow, its only real existential threat in the classical sense (State vs State) is another Corporatist regime, Russia. This adversary, due to its historical path dependence, is economically and socially underdeveloped and institutionally more old fashioned than Germany.
In short, unlike Germany (and the rest of Europe) with its dictatorship of the majority as legitimating façade for its rule by the elite, Russia is a classical strongman fascist dictatorship in which formalities can be dispensed with end Putin rules by brute force and a simplistic ultranationalism, the appeal to long gone soviet imperialism, social ultraconservatism and other crude means of mass control (quite similar to the tools the CCP uses, sans the economic uplift of 300 million people of course).
In the end both regimes, Germany and Russia, work upon identical assumptions: the State ultimately owns everything and everybody within its territory, and there is no limit to the will of the ruling elite. All they need to do is find the right lever within the toolbox of the legitimating apparatus.
That all said (and it was a lot), taking my anarchist hat off and putting myself in the shoes of the ruling Corporatist bureaucracy of Germany, some form of conscription, that is, a period of time where the State, instead of owning 50-70% of your working time as it does regularly, owns 100%, makes sense to deter of confront a foe like Russia. It is consistent with the foundations of the regime, and it's not more egregious than what is already in place. I have no doubt they would rather spend the resources (both money and political legitimacy and will) on other stuff, like they have done these past 40 years but, like they're taught in college, the material conditions are the material conditions, and Putin's Russia is an unreliable neighbor.
Also, I haven't even read the details, but I'm quite sure that regardless of the proposals floated now, what will actually pass, if it does (it will have to beat the Russian and internal anti-Western propaganda apparatus first), it will be not simply a form of military service, but also "social service", which will be the heavily favored option for most conscripts.
I have to say, in a utopian future where a dictatorship of the majority somehow gave me, as Supreme Ruler, a consistent and sustained mandate to reform the Corporatist regime into a libertarian one, I would probably institute a form of mandated military service too. None of that social nonsense, strictly military.
And I would keep it in place until there were no existential threats in the form of Corporatist, classical fascist, or any other form of socialist state-worshipping regimes around my country who could potentially force a regime change on us by an act of war.
For the same reason I would keep a border and strict immigration rules, and would look closely at trade with states and regimes who do not apply similar rules (or lack thereof) to the ones we would apply internally.
These are clear violations and restrictions of freedom and thus incompatible with liberalism, there simply is no question of that. But they would be externally generated ones, out of necessity vs existential threats. Internally, the transition would be total, until the State evaporated completely from people's lives, except in those few affairs mentioned above.
I would call this an acceptable transitional "compromise".
