You don't see any circumstances where someone could be a victim and also a 'member'?
Only where there has been no choice for me.
You read about the child armies in the past being forced into atrocities, attack one of your family or they all die etc... That's a victim and a member.
Being talked around to joining Isis by someone on the internet, that is a bit different, that takes a bit of 'wanting to do this already', then after going there and witnessing the scum at work and not caring about what they are doing, subsequently condoning the leadership for leading them to failure, is very different. That's not a victim. That's a psychopath, a traitor and an enemy of the country..
No matter how much pressure your under, you can always say no, you can always not fly over to another country and be with a member of a terrorist organisation your country is at war with, in fact it's easy, look... I just did it!
We need to go by the law, but much like these few story books that causes absolute morons to commit atrocities on other human beings, it seems our law is open to interpretation. Personally I would use it to keep known terrorists out of the country rather than use it as a reason to bring them back in.