Countering Terrorist Fighters Legislation Bill

Can legislation intended to stop people fighting for ISIL/ISIS/IS/Daesh instead stop people fighting against ISIL/ISIS/IS/Daesh?

The whole question of when the State should be able to step in to stop people going overseas to act on their moral principles - in particular, by fighting for them - is a quite fraught one. As I wrote here;

In which a little spy agency finds that sometimes you can always get what you want, even if its not what you need.

[A note to readers - the following account is a purely subjective reimagination of history.