Sorry to truncate your post, I just wanted to comment on one point.

Surely this is joint responsibility?

For example, if a gang commit a robbery and a victim is killed then the whole gang is guilty of murder?

Might be different in Switzerland; most things are

But there is a difference between being the driver of an escape car, where you cannot reasonably argue that you didn't have some part in the crime , and just being on "holiday" in a country where some nasty things are going on, even if as part of that holiday you get to handle some weapons. Even if you did kill somebody it might have been self defence, seeing there are gun nutters on both sides and you might have innocently walked into the wrong village.

It might be a bit like accidentally passing through Ferguson on a US road trip, and then being accused that I was part of the riots seeing there is no other reasonable explanation of why I went there - but just on a more escalated level.

This is exactly the issue here; unless you agree to suspend habeus corpus, you need to have solid, beyond-doubt evidence. Since you don't in the vast majority of cases, you cannot justify imprisonment or execution, as some on this thread appear to be.

Which presents a very interesting question:

Would you prefer to live in a society where your guilt did not need to be proven beyond reasonable doubt for your imprisonment, but where you cannot imprison all the people you want to, or would you prefer to live in a society where guilt did need to be proven, at the cost of not being able to imprison all those you want to?

The story that Sweden is offering aid has become irrelevant. ISIS is killing anyone thinking of leaving.

https://www.google.ch/search?q=IS+ki..._nA4K6UeTbgvgB

Follow the money
It is rumoured that ISIS people are paid so anybody returning with a wodge......

I prefer to live in a society with a negligible risk of being a terrorist victim?

Habeas Corpus was created at a time when things were simpler.

There weren't many Englishmen fighting on the French side at Agincourt. And even if there were, the king wouldn't be requiring proof that they killed anybody because just by offering their service to an enemy power, they were guilty of treason, for which hanging was the standard punishment.

So is Habeas Corpus outdated? Does it still have a place in modern society? I think it does, and that it should be protected. Often enough, basic rights have been abridged in response to provocations by extremists (Reichstag arson anybody, if you'll excuse the Godwination)? But there is a difference between upholding someones basic rights and mollycoddling them.

The concept of habeus corpus is nothing to do with combatants on different sides; it is as simple as a measure to prevent unlawful detention, and has been a cornerstone of many legal systems for hundreds of years.

If we now say that we will imprison people without actual proof, we will be suspending that right. That is a gross erosion of our freedom.

And is it outdated? Absolutely not. Habeus corpus is a concept in law, applicable to all offences. It simply weighs the proof against the punishment, and therefore supports the 'Innocent until proven guilty' mandate our legal system is governed by. That is something that we absolutely must not contradict, no matter how much fear is sown.

Granting basic rights to those we would prefer not to, and mutating beyond recognition the cornerstone of our law is not mollycoddling, it is the cornerstone of civilized society.

Then you're on the wrong planet.

Of course not, but in this particular case we are discussing whether Habeas Corpus protects people who have gone away to fight in a foreign war, and are suspected of commiting or being complicit to war crimes, or at least acting as mercenaries.

It must.

Being suspected of something is never a good enough reason to be imprisoned.

Of course it is. That is what arrests during trials are for.

Being suspected is a good enough reason to be imprisoned, of course, pending a fair trial in the near future.

Locking up someone without a trial is where the erosion of freedom begins.

In Switzerland it is; foreigners are almost never given bail so they sit in prison until the day of their trial.

Interesting article here on this leaving ISIS topic (in German).

Surely being suspected of something is never enough to justify removal of liberty...this can only happen after an accusation is made?

Depends if they have a prosecutable case, and the stakes at risk. If there is a risk to public or national safety, they could certainly hold someone even as they gather evidence.

Here's a case of Norway banishing a terrorist to a remote village:
Norway banishes Islamist preacher to remote village after prison release

This particular court decided basic national interest takes precedence over his right to a family and free movement.

Unless one is a paedophile Polish film producer.

Presumably, if they believe they have a prosecutable case, THEN they accuse the suspect, then we go from there.

The Islamic preacher isn't being held in any way, he still has his liberty to go about his business in the area where he lives. This is a similar punishment to revoking someone's right to travel outside the country, but on a micro scale, of course.

That is quite true for civil and criminal laws. International terrorism crosses over to public safety and national security issues, and could be handled differently. Law enforcement and courts are given some discretion in assessing threats, preventing them, then finding the due process for prosecuting them. These take precendence over individual civil rights. In the US, under defence bills, terrorist suspects can be held without trial. Other countries also have similar grey areas between these.

Good point. I think in the US they can be held indefinitely?

In the UK, normally you can only be held 24 hours for a normal crime, or 36 for a serious one. A judge can extend this up to 96 hours in extreme cases.

We have a similar terrorism (civil liberties erosion) act which allows up to 14 days without charge.