Claim: Crime plummeted as America browned

No it didn't. The opposite is true. America was 88% white until hart-cellar. Violent crime soared in the decade following hart-cellar and the civil rights act and stayed at that level for two decades. It finally made significant movement downward in the mid 1990's due to changes in law enforcement techniques and now its increasing again.

We should only use the murder rate to measure violent crime. No other violent crime statistics should be considered because they are too easily manipulated and also are a function of reporting. Murder rates are hard to manipulate for the obvious reason that dead bodies have to be mostly accounted for.

Secondly, fluctuations in the violent crime rate are entirely dependent on the change in behavior of young black and hispanic men. Other groups don't commit enough violent crime or vary enough to move the needle.

Tldr: The end of legal racism and control over blacks resulted in a two decade long crime spree by blacks.