If you're gonna argue like that, you must include the Reds (The Cueto/LaRue incident), Giants (Marichal/Roseboro), and White Sox (never forget 1919). Point is, every team has a bad moment. And to your other point, I've lived in New York City my entire life and I can't stand the team and their asshole supporters. And I'm totally cool with the Mets.
I've never understood why so many New Yorkers hate the Yankees but love the Mets. They are teams from the same city. Because there's two of them do people feel they can pick and choose? It doesn't seem right to hate your hometown team. Maybe some like the Mets more because they're the underdog, but that doesn't make the Yankees the Great Satan.
What makes the supporters "a*****"? Is it that Yankees fans are seen as more Italian or working class? I don't know the answer but I find the hatred of the team to go beyond mere sports rivalries.
Every sports team from Massachusetts is a garbage team.