I disagree. If we look at the 70+ jihadists that are being spoken about, these are individuals who have been released from prison having previously serving sentences for terrorist related offences. Up until Friday lunchtime, none of these had come to the attention of the authorities for any wrong doing. So you could argue that they were under the most stringent of control measures, or had changed their views.
Of course, one such individual has then gone on to kill 2 people and injury others. We need to understand what changed. But it is possible that excluding someone from "normal and reasonable society" actually makes the situation worse.
I have seen many people who would die for their cause whilst terrorising others, and the most dangerous were actually part of the animal liberation front rather than religious fanatics. Most are very young when they start out, teens or early 20's. Their offending builds and they often cycle in and out of prison. Yet, over time their views soften and they come to realise that violence is not the answer and they fit in to 'normal' society. I'm by no means naive enough to think this applies to everyone but do fundamentally believe that everyone can change.
I would have dearly loved for things to have been different on Friday, but as heartbreaking as it has been, I still think that Jack, Saskia and others were doing the right thing.