If they have broken the law, they should be dealt with. Once they have served the required penalties for breaking the law, they are free to resume their place in society.
'Links with radical networks' need to be very closely and very carefully defined. Identifying as a specific religion and going on holiday to a high-risk country aren't 'links' to anything.
They haven't committed any criminal acts nor is there any reasonable suspicion that they may.
Even if they have sufficiently evidenced links to 'radical networks' (and I don't even know what that means; I might be classed as a radical for thinking that our government, election systems and a large chunk of laws are not fit for purpose and should be dismantled and replaced) they should be surveilled, not subject to being randomly arrested and deported.
Yeah, probably. I'd be happy that I lived in a society that didn't give in to paranoia, despite being force fed it by news outlets and officials who seem to actually want you to fear and hate people who want to be feared and hated so it proves their point that they're feared and hated. If the security services weren't doing their job when it was in their (existing) power to prevent it, that's a problem for the security services.
You're rather grossly missing the point that it's just not relevant to me, or you, or anyone but the security services what the actual reason was that some dick blew themselves up with some other people. Knowing why or how they got to that point has no meaning to any of us - the end result is that some dick blew themselves up with some other people. The security services need to know, but the targets and victims (us) don't.
As such, the information about who they were and where they've been is meaningless and there's no reason for it to be published or yelled at you from TV screens. It serves only to fuel hate and fear, to the point where some people will happily extend the powers of the security services to just straight up ignore hard-won freedoms. That's then used as evidence of hate and fear, which is used as propaganda by the hatemongers and fearmongers, so more dicks blow themselves up with some other people.
Well done, you just managed to create the exact situation you were afraid of by your fear of it.