First of all, here are some reasons when it is NOT a mortal sin to drop your team:
a) The team leaves your city. (i.e. Hartford Whalers to Carolina)
b) The team is really bad and it doesn't even seem it they are trying to win. (i.e. the Pittsburgh Pirates or Kansas City Royals)
c) The team becomes difficult to follow because of your geographical location. (This issue was more of a problem about 10 years ago but even today it is tough to follow a West Coast team in the Northeast)
d) The owner is incompetent. ( i.e. Washington Redskins or Oakland Raiders)
Here are a few rules that need to be followed:
1) You cannot abandon a team if they have won a championship within the past five years
2) You should take a mourning period of half the period of time you were a fan of the team. ( I liked the 49ers from the age of 7 to 17 so that is 10 years of fandom then I waited 5 years before starting to support the Giants.) It is important to clear your head.
3) If you move to a new city you can adopt their team.
4) You can never change your allegiance to a rival of your 1st team. (If you like the Sox you can NEVER cheer for the Yanks) Dan if you decide to leave the Skins you have to leave the NFC East FOREVER.
5) You cannot hop on a bandwagon. (In my defense started to like the Giants in 2006 and they won a completely unexpected Superbowl in 2007 and the Giants were only 10-6 that year.
6) You must commit a minimum of 5 years once you decide to support a new team.
It will probably happen to most fans at least once in their lives and I believe you shouldn't be penalized your entire adult life for a decision you made when you were 7 or 8 years old. The important thing is to consider your opinions and make a choice you will be proud of for many years to come.