For months....the interior department of the German government has been reviewing options on how to make it awful hard for a resident German (of whatever variety of religion or mental status) to leave and go off to war in Syria.
By late Wednesday of this week.....as various journalists report today in the German news.....there will be a submission of a bill going through the Merkel cabinet for a modified law. The travel opportunities in the future would require you to have not only the passport but the identity card. The intention is that if they figure out you left for a forbidden area....they'd revoke the identity card (an exit lock type system). In certain words.....you just wouldn't be able to return.
Now, this has unsettled some Berlin political folks.....notably mentioned is the Linke Party, which says that entry for a German citizen is a fundamental right. You can't stop a German from crossing the border.
My hunch is that if you made it back from Syria (for example).....you'd enter into Turkey or a bordering EU country.....and at the airport, they'd ask for the two forms of ID. In the database, they'd see that the identity card was revoked. At that point, even with a passport....you couldn't fly into Germany or Schengen state.
Schengen states? Well, this is a term that gets thrown around....meaning a group of twenty-six European countries which formed a 'code' and protect each other from illegal entry. This goes back 1985, with a much smaller group who determined that they could streamline the process and more easily deny entry.....if everyone operated with the same rules and philosophy.
If you look over a map of Schengen states....it's ALL of western Europe. The former Yugoslav states are still outside of the zone.
For the typical American....without a visa....you often fall into the Schenegen rules if you aren't part of the NATO establishment. For example....without a visa.....I could only visit Germany for ninety days, and then I'd have to leave for ninety days before I could come again for a standard visit. If I violated the ninety-day limit.....they could curtail me from re-entering for an extended period.
My hunch for the Islamic Germans running off to the war and getting frustrated or demoralized? Well....if they know your name....your ID card would become a problem, so you couldn't fly out. What happens then? Would Turkey accept these Germans? No one has said anything about their attitude. Legally, would the cancellation of your ID card trigger the German court to get involved? The projected idea is that the court would be the heavyweight anchor of the cancellation of your ID.
A German stuck outside of Germany? In essence.....yeah.
I think the whole thing is to make this as difficult as possible, then advertise it as far and wide as possible, and then enforce it. Maybe a year or two down the road.....enough people have surveyed the dozens stuck in Turkey and no remedy for them ever coming back, thus changing society and attitudes.