Re: Bias in, bias out
it is the old correlation != causation coupled with structural inequalities.
If you have data that shows a correlation between skin colour, home postcode or whatever with criminality then if you have a limited budget it makes some sense to deploy your resources disproportionately at that demographic. You will get more 'hits' for your money which reinforces your sense that this is a good approach so even if the original correlation is based on historical discriminatory policing your approach may appear valid. If the affected demographic is relatively poor and under-represented within the planning process then it is even less likely that a discriminatory approach will be called out.
A counter-example would be for a financial crime unit to adopt the approach of kettling the Square Mile and shaking down all the white guys in suits. They may well achieve a better hit rate than random selections but as well as being as unfair as harassing black people you could expect more successful push-back against such an approach due to the way power structures work in society.
Intelligence led policing might be even more successful in percentage terms. Now ask yourself if non-causal correlate led policing is likely to reinforce cooperation in the community most likely to have useful insights to share,