Okay, technically, fighting isn't allowed; the players involved will get five minutes in the penalty box for dropping the gloves and sometime more. But fighting rarely gets one ejected from a game, and I have yet to hear of a player being suspended for a fight.
So on some level, yeah, fighting is accepted in hockey.
Sometimes a player will want to fight to send a message not to mess with the stars on the team. Take a run at someone like Ovie, Stamkos, or Crosby, and you'll have to answer to one of the enforcers.
Sometimes a fight can spur a team to come back and win a game.
And I think sometimes when a game builds animosity, two players will duke it out to defuse the tension.
As others have said, hockey is a fast-paced, highly physical game where the action is almost constant. Baseball is incredibly slow. Football goes in little tiny bursts of energy. Basketball is a little more constant, but...