This is not the legal standard at all. It is very specifically not based on the perception of the officer. It's based on whether a hypothetical reasonable person would have taken those same actions.
The ICE officer probably won't testify or share their feelings. And if they do, the standard is still based solely on their actions viewed through the lens of this hypothetical reasonable person. The defense will argue that they justifiably feared for their life (or whatever their statutory standard is), but the officer's claimed perceptions are irrelevant.
Imagine an insane cop shoots someone because they think they're a space alien trying to probe them, but it's actually just some guy trying to stab the cop. The reasonable person standard means you'd assess the shooting based on the supposed actions of a reasonable person. Would a reasonable person have shot them? Probably. So, even if a shooter is motivated by the delusional belief that their target is a "space alien" intent on probing them, the act is legally justified if the target was posing an actual, objective threat—such as an attempted stabbing. Because a "reasonable person" would use force to stop a knife attack, the shooter's bizarre motivation does not negate the fact that the use of force was objectively necessary. In this case, the subjective fear of the officer is irrelevant if the act was objectively unreasonable.
And, yeah, of course the courts bend over backwards to suck cops' dicks and they get away with murder all the time. But, honestly, how many cops are even criminally charged? At trial, in front of a jury, it's harder to prove. We just usually don't see indictments and when we do, often important evidence is excluded in favor of law enforcement.