The post above claims that homicide rates started to go up "during the previous administration" (i.e., before January 2021) / "in the summer of 2020." The article you're linking is from May 2021, and talking about decarceration, not homicide rates. That seems like it cannot possibly be evidence for the claim that decarceration causes increased homicide rates.
I know correlation is not causation but homicides tend to be committed by criminals — ie those with one or more prior in offenses.
I agree nbc is pretty terrible at reporting and apologize for posting them rather than a reputable source but google gave me that so I posted it.
There was a definitive villainization and backing off of police nationwide that corresponds with the rise in crime. A lack of police action, coupled with COVID stressors, is a recipe for rising crime.
My belief is that the murder spike has nothing to do with the police, and everything to do with covid and the economy. Violent crime was already spiking before the george floyd murder, for one thing. Cops do very little that prevents murder, they mostly just arrest people after them, for another. But that's just as arbitrary as your interpretation. Without data, we're just making up stories.