As others have mentioned, context matters a lot. The arrested group came back from Syria (where they fought alongside YPG against ISIS) radicalised, and were monitored ever since then. Their alleged crime isn't using Signal, it's just that a French anti-terrorism law allows to be arrested for "organisation with the intent to commit terrorist acts", which the DGSI(internal intelligence services) claims a radicalised g…
>context matters a lot Not in this current context. You can't detain someone willy nilly for 'intentions' without such intentions being explicitly stated as proof in letters, emails, messages, threats etc. This is authoritarian pandering 101.
AIUI that's lawful in the UK, you can detain people under the terrorism act with only suspicion of intent. It does make some sense, it weighs the level of evidence inversely with the potentially large-scale of awful outcomes. (My understanding hear may be flawed/wrong.)
In order for that not to slip into fascism you need a forthright government that is honourable and believes in the rule of law ... both things the current UK government has proven they do not have.