Yes, the speed is exactly the problem. When we meet someone who looks or behaves differently from what we expect it may take a few seconds for us to process what our response should be, e.g. wait - see what this person is about before making any judgements.

But we have fast acting lizard brains and slow acting human brains and when there are swirling emotions - fear etc then we might act before the human brain becomes engaged.

Does this other person have a gun? I have a gun, the whole thing is over in seconds with maybe drastic consequences.