Mandatory military service is a huge breach of personal liberty. That is why there have to be really good reasons for it, not just something like teaching young men discipline. In case a country is under threat of an invasion, mandatory military service can be justified and can indeed contribute decisively to the defense of a country. Of course, at the time the invasion occurs, it is too late for such a measure; that is why the risks have to be analyzed well before.
Currently, after the end of the Cold War, I don't see such a risk in most Western countries. Today's threats are different, e.g. terrorist attacks or attacks on citizens or institutions abroad (embassies, ships, etc.). In part, military engagements abroad to defend a country's interests may be justified, but as they are not directly related to the defense of one's homeland, they don't justify mandatory military service. Even if we don't consider civil rights, a professional army is much more capable of controlling such threats.
Reading some of the posts in this threat I wonder about the life experience or the lack thereof of some of the posters. When I had to serve in the military, I experienced it exactly as I wrote above - a huge breach of my personal liberty. For the first time in my life, I had lost my freedom. This is different from mandatory schooling or working at a job. Some of my comrades decided that the conditions under which we served were so bad that they just didn't show up any more. So they were chased by military police, tracked down like criminals and put into jail.
Germany has now paused military service starting last year. This means that the law still remains in the constitution, but the implementation is now paused for the time being. In reality, it comes close to abolishing military service, and I don't see any chance of it being reintroduced in the next decades. Which is a good thing. In fact, I was astonished about how long it took the government to come to this obvious conclusion. Didn't the Cold War end in 1989-1991, with the last Soviet Soldiers leaving Germany in 1994?
Besides the breach of personal liberty, there was another problem with German military service: injustice and inequality. Many people dodged military service, and we as the conscripted felt like the nation's idiots. The problem was twofold: First, many people avoided military service by conscientious objection. In principle, this is of course okay, and many of these men did a valuable (and difficult) job in hospitals. But many of these conscientious objectors actually got very easy-going jobs, often abroad and with no real effort involved. Nothing like being chased around by drill sergeants. Second, many men dodged mandatory service altogether, often on alleged health reasons (yes, there are many examples of professional sportsmen being unfit for service). I still feel the injustice when I read CVs from persons who were smart enough to avoid service, whereas I have lost a year in my professional career due to my honesty and sense of duty.
So please keep all this in mind when discussing such a far-reaching issue.