Someone taking weapons somewhere (regardless of the cause) is always a dangerous person. Regular soldiers included and the government treat them as such. It's an unfortunate position (of course) if that person is fighting on "your" side.
Yes, but the problem here is not that, it's the arguments used to build the case.
They have not been any evidence of criminal activities by those people. So far, all what they have against them is "they are protective about their privacy".
That's a terrible reason to arrest and maintain people in jail.
It's grounds for having your citizenship revoked unless it will render you stateless. People suspected of being on the way to Syria would get their passports confiscated.
Nine EU countries made similar rules, though I don't know how many still have it in effect. Any citizen/resident of Denmark is still prohibited from going to the conflict zones of Syria and Iraq.
