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.
A crime is not something you evaluate morally. It has a very narrow definition that is codified by each society it is been judged in.