Regarding the motive to bring it to bring the perverse incentive to light, it is possible that an institutional cover-up exists nationwide, but highly unlikely given the Christian Ethos that existed in this country...
If that is the case, and a perverse incentive exists for cops to arrest the innocent, then we should see this occurring all over the country and across all racial groups
Non sequitur - we'd see it only if it were commonly the case that someone who knew of it had motive to bring it to light.
I showed that your conclusion doesn't follow from your premise ... which is what "non sequitur" means.
Regarding the motive to bring it to bring the perverse incentive to light, it is possible that an institutional cover-up exists nationwide
Red herring. There need be no nationwide institutional cover-up, only a collection of local 'blue walls of silence' - against which our battered Christian Ethos is far-from-reliable protection (IMO you were more right than wrong when you said it "existed", past tense).