Are you actually comparing paying for healthcare, infrastructure and social security to military service? That’s pretty ridiculous and I think you know it.
Mandatory military service is absolutely not necessary for the sake of society. In Norway, for example, around 80% are released from service and it’s doing quite alright. Sweden is doing fine, too and only a portion of eligible people are actually called in.
And you’re just glossing over the fact that the overwhelming majority in Finland would still serve if it wasn’t mandatory, according to polls the willingness to serve has never really dropped.
And regarding the civilian service, I went there. It’s a year for everyone, instead of 6 months minimum for the military. You also get paid the same as the fresh recruits in the military, which is simply not enough for a civilian. You try living with the day wage if you don’t believe me. And that pay is for a 40h work week. Those conditions are in places worse than the conditions in open prisons, like in Suomenlinna for example. So civilian service is in essence a prison sentence.