The guaranteed next step is to offer the volunteers a long term paid contract at the end of their term. This would probably be well above what they would be paid elsewhere (young men with no university degree, desperate enough to volunteer in the first place).
Run the scheme for a few years, and you will have a large number of, young, high-school-level educated people that are financially dependent on the army. Thus, a militarized society.
What could possibly go wrong?
Finland, Sweden, Norway, Switzerland, Austria, Brazil, Chile, Mexico and Thailand each have active conscription [1]. The slippery slop you describe is far from inevitable.
Also, if you have decades of mandatory conscription then there is no slope to slip. Germany on the other hand is now on a slope, since they regress from a fully professional army back to conscription. How much down they will slip, remains to be seen.
Active != mandatory.
> Mandatory conscription (which I have personally served) is for a fixed term, so your livelihood is not tied to the army paying your salary
You're seriously arguing that countries with mandatory conscription are less militarised than those with active (but not mandatory) conscription?
On top of that there is a large dislike in the society against military system. To break that you won't just need "a few years", but likely ~2 generations of compulsory military service for both men and women (e.g. how Isreal does it), that forces a personal connection with the military for everyone.
And even with the new voluntary service the armed forces will be much smaller than the army of just West-Germany alone during the cold war (which was about 0.5 million).
It's time to wake up to the fact that the Cold War actually never ended.