I think this racist talk about Boston is a bunch of media crap--probably started in NY or LA where Celtics hate runs deep.
Boston, of course, is no different than any other American city. Actually, it's a liberal Democrat town (the Irish mayor is now working for Biden). Sure there are pockets of conservative working class types, but every city has those.
The Celtics broke the racial barriers in the NBA. First drafting an African American, then having an all-African American starting 5 (Can you name them?), and finally having the first African American coach, Bill Russell, in a major sport.
You have to be careful about interpreting all the race stuff. Keep in mind the Celtics dominated the NBA so long in the 50s and 60s, winning about a dozen championships in a row, that they built up a lot of resentment in other cities, especially NY and LA, and also Philly. The Philly sports media is pretty hostile to Boston teams as well. The Patriots, by the way, have been getting the same treatment lately, from the same sources (primarily NY, ESPN, etc). They have also just won too much.
Jaylen Brown? He's just a kid. A smart kid, but he doesn't know the history.