Do you believe that black people viewing white people as a potential risk, and altering their behavior to mitigate that risk, are bigoted racists making judgements based on irrational fears with no basis in reality?
Every bit as much as white people who do the same.
Aspersions and doubt can wait until treatment turns sour, and everyone deserves the benefit of the doubt.
As soon as treatment slips into suspicious behavior, that's when the hackles can and probably should go up.
Then, I think the hackles should go up the minute, the second some cop starts treating the a person as if the cop identified them as a "black person" or "an undesirable", or whatever else.
I don't usually get treated by cops like that but I felt the same way, for myself AND my wife, whenever cops harassed my ex-wife. It's not about "cop" specifically but about the things cops do and the way they do them.
For the same reason that I treat people as fairly friendly until they start talking about "doing something about over population" without specifying what that is or some other dog whistle, there are a wide variety of behaviors distinct from "just being there", from glances and looks, to attempts to initiate interaction given a wide variety of tones.
Just being there, just being a cop, is not and should not be enough.
The number of cops makes a statement, the actual pattern of their behavior, but not their mere existence.
I would react very differently to a group of people walking towards and probably past me on the street, than I would to a group of people who as they are walking towards me begin to fan out in my path.
Context and behavior matters, as does situational awareness.
It always matters. Acting on mere paranoid assumptions rather than observations is bigoted, racist judgement.