You're absolutely right about the coming reaction. There will be a reaction, and it will be focused on the people who are least prepared to defend themselves (because fascists would rather pluck the legs off of spiders than fight fair). You're also right about adventurism. It is often counterproductive. Edpecially in a society where the media is dominated so completely by the bourgeoisie. The propaganda of the deed rarely (though not never) accomplishes as much as the resulting bourgeois blood libel.

That said, we need to be careful about blaming whoever did this for the backlash which follows. The backlash is the fault of nobody but the people giving and carrying out the orders. The worse the backlash is, the more justified the original assassination probably was. Collective punishment was a cornerstone of the Holocaust. Collective punishment is not the prescription for lone wolf terror attacks.

If this is an actual case of left adventurism we should emphasize that these actions indirectly impact millions of lives. This is not a fucking game. Liberals treat politics like a game. We know better. On the other hand, we're staring at societal collapse on the horizon and spontaneous shit like this is only going to become more common.