The national crime victimization survey largely agreed with the FBI's Unified Crime Report (on matters of race and violent crimes, anyway). The latter is data collected by policing agencies and the former comes from victims. If law enforcement discriminated against Blacks, we would expect a discrepancy between these reports (it's possible that the victims are simply "equally racist", but given that the victims of black offenders are themselves overwhelmingly black, this is unlikely). Also, there have been a few other studies like this one[1] which don't find anti-black bias in sentencing, conviction, etc. This doesn't mean it doesn't exist, just that the conclusion of a racist criminal justice system is not entirely supported by the evidence.

One anecdote about the weed thing, since that comes up so often--I live in Chicago and apart from festivals, I never see white people strolling around downtown smoking weed, but I do see this probably once a month, and the user is consistently black. The white people I know who use marijuana do so at home and out of public view. This is just an anecdote, but cultural differences in usage could better explain the arrest discrepancy than police racism. At least I would like to discontinue the trend of assuming that every gap is necessarily and automatically attributable to discrimination.

[1]: https://www.researchgate.net/publication/256079484_No_eviden...