Why is Fighting in Hockey Allowed?

Look, I love violence as much as the next guy.  I will also admit right off the bat that I do not know too much about hockey.  In fact, I will start to actively follow hockey (and the Minnesota Wild – random, I know) next season.  However, for as long as I can remember, I’ve always wondered how the hell the NHL allows fighting.  I understand that fans want to see it, and players don’t want to stop doing it, but these are not valid reasons for fighting to continue.  I’m sure Kobe Bryant wanted to knock Dahntay Jones’s lights out after he blatantly tripped him, but he didn’t.