There's a specific reason for why the giants are trying to kill you.
The Goose (or Moose) is simply trying to protect her young.
The Dragonfly is a hungry fellow, simply creating ash to eat.
The Bearger is getting ready for the winter, packing on as much pounds as he can.
But what of the Deerclops? Why does he kill? He has no young, and has never been seen to eat anything.
The answer is simple; he is angry. Maybe once he had a family, and a happy life as well. But something must've happened to his happy life, something that caused him to snap. He seems like an intelligent person rather than an animal to me, but a very bitter one, one who is so full of sadness and hate, that he is envious of the player.
He does not do this out of spite. He does it because he has no self control. He longs for the sweet release of death. But They will not allow it, because it interferes with their petty little game.