Doing exactly what is needed to get change to happen when the cops are murdering children in traffic stops by shooting them in the head and then lying about it at every single level of power is good actually.

When the state refuses to provide justice people should absolutely take it. The threat of the population taking their own justice is precisely what motivates states to provide a source of it that they control.

The translation is wrong, you can see his actual tweet in this article:

Les chiens de garde nous ordonnent d'appeler au calme. Nous appelons à la justice. Retirez l'action judiciaire contre le pauvre Nahel. Suspendez le policier meurtrier et son complice qui lui a ordonné de tirer. Foutez la paix à l'ambulancier.

He did NOT ask to hang the policeman, he said "suspendez le policier" which means put the policeman on administrative leave (second definition here)

If he wanted to say "hang the policeman", he would have said "pendez le policier" (third definition here)

The translation given here in this article is voluntarily misleading. I would invite you to paste the original tweet in DeepL or ChatGPT to have a more accurate one.