I have just heard time and time again referees saying things like "I don't want to decide the game (by calling penalties)," but a linesman would never not call icing because he doesn't want to affect the game.
I just find it interesting that there is that culture in hockey that penalties are the refs' fault, and yet icing is the players' fault. I feel like the question in the OP probes that a little bit.
Marginal ones. Neutral zone ones. Penalizing a player who illegally takes away a scoring chance is fine.
Penalties are often subjective. Icing is more black and white.