The thing about the NBA is that every foul call could be considered subjective. Charges vs blocking. Offensive, or defensive. The player dribbling the ball is warding off the defensive player with his other arm (a foul) the defensive player is constantly reaching into get the ball (a foul) the player dribbling is always cupping the ball (considered carrying or traveling). Every shot is contested and potential fouls can called on every possetion. Add the fact that the game is extremely fast moving and you have the ingredients for a very difficult job.
Since calls can be made either way, and the difference between the call going one way or the other very small, it's only understandable that the crowd can have a huge influence on way the game is called.