Why have a trial if it becomes a show or ritual that rubber stamps a verdict that everyone is convinced of from the very start?

Hannah Arendt agreed with the verdict that Eichmann was guilty and that he should hang. And yet she disagreed with all reasoning on display in the trial, whether it was from the prosecution, the defence, or the judges. Given the problems that Arendt identifies with the trial, some may wonder whether it would have not been preferable to simply settle matters outside the courts. As Arendt points out, instead of capturing Eichmann and flying him to Israel, the Israeli agents could have killed him right then and there in the streets of Buenos Aires (ep:15). Still, despite all the problems with the trial, Arendt also disagrees with any such extra-legal solution to the Eichmann case. On the contrary, she makes her view clear by the end of her book that, despite the profound flaws with the trial, it was nonetheless utterly vital for the future of humanity that the Eichmann trial took place.
How do you make sense of Arendts position? Why have a trial if it becomes a show or ritual that rubber stamps a verdict that everyone is convinced of from the very start? How do you think through Arendts view that the future of humanity depends on holding trials to prosecute crimes against humanity?

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