I don’t think there is anything wrong with rooting for a sports team, though with several caveats:
1.) Proper context and perspective must be maintained. Many sports fans feel jubilant after their team wins, and depressed after their team loses. Some people feel real hatred towards their team’s rivals, or the rival team’s fans. I think all of this is wrong; it’s just a game, and should be seen as such.
2.) I think a person should root for their team, but not wrap their identity up into the team. This goes for other things too, such as career, school, etc.
3.) Watching a game on television or attending a game can be problematic, due to exposure to pritzus or coarse behavior. This might be a problem with some sports (football) more than others (baseball?).
I personally do follow several teams, but I don’t watch games on television (don’t even have cable/antenna television). I read the recaps and analyses, and sometimes watch the highlights online.