Meaning of movie?

Ok...first thing GREAT movie watched it 4 times and about to watch it a 5th after this post. Thanks to all that made the movie possible. I've read many threads and post concerning the meaning of Promethus and I feel all were wrong when it came to the meaning why the so called engineer started killing the crew. My opinion the engineer killed the crew because it thought Shaw was in danger after the getting hit with a gun. I don't think the engineers plan is to kill off the humans. In the beginning of the movie the engineers made the altimate scarfice and retuned to earth after that helping the humans. Just my opinion of one scene