There is no word that can properly encapsulate the crime being perpetrated against all present and future life. Ecocide? Omnicide?

The priority isn't getting justice for this; the priority is stopping it. Often (and I think this is why Mao's sentiment is echoed in a bunch of other revolutionary writings) the quickest way to stop the harm is to give the perpetrators a way out. If you tell people you'll kill them whether they fight or surrender, what are they going to pick?