In philosophy land, beliefs have to be earned- beliefs have to survive criticism and meet challenges before you get to have them. That's how I look at it, anyway.
I don't think sports fandom should be any different. (I often tell people that even had I grown up in New York, I would have seen the light and been a Sox fan anyway.) The test for deserving to stay a sports fan? This Onion satire from January. If your dignity survives intact, you've earned the right to keep rooting.
And in honor of Friday's starting pitcher, another old Onion piece.