I think it's reasonable to say that 4/5 black men 25 to 44 is likely not warranted and is probably motivated at least in part by racism.

I don't think that's obvious at all. 4/5 sounds high, but that's a lifetime stat. To put that in perspective, let's work out the minimum chance of being randomly stopped by police per year that results in an 80% lifetime rate.

Let's assume that the black male population is evenly distributed in age between 25 and 44, making the mean age of that demographic 34.5 (in reality the mean is probably higher, as our general population age distribution is left skewed). Let's also assume that the mean age at which people start going out in public unaccompanied by a legal guardian is approximately 16. That number would be difficult to find proper stats on, so I'm intentionally high balling it. That gives an 80% chance of being stopped by police at least once over a mean interval of 18.5 years.

Now given those assumptions, what's the minimum chance, per year, of being stopped by the police in public that produces that statistic? This is easiest to calculate by finding the yearly probability of a stop that gives a 20% probability of never having been stopped after 18.5 years:

0.2 = ((1-p)^18.5) p = 0.0833 = 8.33%

That gives an 8.33% chance per year of being randomly stopped, and a mean time until a random stop of ~12 years. That doesn't seem terribly outrageous to me, and roughly matches my experience as a white male living in Ottawa (2 random stops over ~15 years of adulthood).

I'm not saying there definitely isn't a problem with racism among police. I just don't think it's reasonable to point at this stat in isolation as a smoking gun. It needs to be put into context through comparison with the chances of police interaction for other demographics, and comparison with the rates of criminal activity among other demographics, among other things.