In my side job I get to talk to sports fans from all walks of life, all colors of skin and all parts of the country. Living in Florida and me having a thick Boston accent, they know where I am from.
What they all comment about Boston sports fans is that we are hard core, entitled, pompous a$$holes that are devoted to our teams and that we travel well. No one mentions racism.
The non Tampa fans(Tampa is called Champa Bay down here) comment about the amazing success of all our Boston sports teams and wish their teams were so good.
There's definitely some racist stuff that has happened and been said in the Garden and Fenway, but from my numerous talks with sports fans across the nation, people I have talked to don't see Boston sports fans in that light. Maybe it's because those racist things that happen and are said everywhere.
This is just me postulating this but that is what I think from my experiences talking to sports fans from everywhere and also going to games of various sports in San Antonio, Austin, Cleveland, Baltimore, New York, Philadelphia, Boston, Orlando, Jacksonville, Miami, Tampa, Chicago and Washington DC.