The Engineers never had a plan to kill the humans.

When the engineer woke up near the end of the movie, he didn't understand the language of the humans and he seemed rather intrigued by them. I think that if they had a different approach he would have been nice to the humans. An important clue about this is when the old man's daughter tells him that every living creature must die and that it's the natural course of things. That quote wasn't there for nothing The engineer, being so much smarter, knows that immortality would only destroy everything. All living creatures must return to the soil one day to contribute for other life forms and let the natural cycle continue. As soon as the robot talked to the engineer in his language, the engineer realized how corrupted these humans were (he associated them all together) because of the intentions of the old man, so he immediately judged them dangerous for all life. These engineers were rather the bringer of life than the bringer of death. The planet you see in the first scene of the movie is Earth not inhabited by any animal life form. The engineer drank a different kind of goo that destroyed him and created various life forms into the water. Many years later when those life forms evolved and created a complete ecosystem the Ancients returned to Earth to colonize and the humans are their direct descendants. I think they acted this way to escape a war. In the holograms inside the engineer's spaceship, you see them running away and they're scared. Their home planet was probably invaded by the predators or something else and they've been colonizing other planets in hope that their species doesn't die. When they examine the head, they see that it's been dead for about 2000 years. 2000 years before would be the birth of Jesus. That ship we see in the movie didn't make it but maybe another one did. They clearly had something to do on Earth and I doubt that this was the only ship headed there. Now putting everything religious aside, Jesus was a very knowledgeable person who'd tell people not to drink water in a river that has dead animals inside and other stuff that today is obvious for us but that wasn't back then. That 2000 years number isn't there for nothing in the movie so that's why I think that the Ancients actually had a peaceful mission on Earth. Having a refuge and bringing wisdom to its own people who lost all knowledge of their origins over time. The sculptures the humans found are testimonies of where they actually come from rather than where they should go. The plan to destroy humans was only a bad interpretation of what happened by the main character. What do you guys think?