The question here isn't their actions. It's their motives. There's a South Park sketch where the kids are out camping with the local gun nut, and he explains

The question here isn't their actions. It's their motives. There's a South Park sketch where the kids are out camping with the local gun nut, and he explains that they're not allowed to hunt most these animals - but they can act in self-defense. So he teaches them to shout "it's coming right for us!" before firing. ( https://www.youtube.com/watch?v=Nt6kKhlX8vU https://www.youtube.com/watch?v=Nt6kKhlX8vU ) So what the grandparent is alluding to, isn't whether it's correct to act appropriately if "it's coming right for us!". It's the culture of "stop resisting" used as robotically as your Miranda rights to later justify an escalation of violence. No-one's saying an officer shouldn't be allowed to respond to threats appropriately. We are saying we should be able to trust officers not to imagine threats for the sole purpose of justifying such an escalation (which, if taken at face value, is what the OP article describes). And yes, you're right; other than taking the protagonist's word for it, it is exceptionally difficult to prove one from the other. That's what makes the prospect so troubling.