Engineers want to destroy Earth - or only humans ?

Why we destroy plants that we harvest? I think the same reason engineers have for killing humanity before it gets stronger than the species top in the hierarchy. Imagine Coke bottle questioning the plant manager - questions about his or her origin and where to go from here and to ask other free will questions. ;)

I would guess it would effect everything. That's where the worm/Alien came from. Everyone is using the word evolution in conjunction with the goo. I would argue more of a Borg assimilation goo. It almost seems as thought it grabs available code, strips it down to some base senescence [big, good, evil, tentacles, instinct] and recombines it to the existing code pool.

The black goo would be world destroying. Everything would get humped and mutated and then die off resetting the "petri dish" for new experiments......like "The Mole People".....

The goo would affect everything as seen in the movie - the sacrificing engineer, the worms, Holloway himself and his sperm in shaw, Fifield. I also think that the decapitated space jockey mustve been infected with it too, because when they reanimated his head, it also reanimated the virus which caused his head to explode...which I think wouldve happened to Holloway eventually.

Whatever their motive, invaders would wipe out the highest form of life to preserve the planet for their own will. Why destroy a perfectly viable world?

OK, not all life would perish as we saw that the ancient xeno was only capable of gestating via the larger mammals (medium to large dogs & humans; but why not lions, tigers and bears...oh my! ; P ). Unfortunately, parasitic domesticated house cats, being too small (except for maybe some fat ones), would unfortunately take over the world as they've been trying to do for ages (and succeeding in most cities). ; )

@abordoli It's highly possible that' xenos from smaller animals would lay smaller eggs for smaller face huggers.

I agree with TheNextLV426 about the sizing of the facehugger. The XenoMorph always is sized and has characteristics of the gestating host. However, why was the squid so large? It was from a human not an engineer. It even seemed too large for an engineer unless it knew it needed the size to wrestle one down. The goo itself seems to be ebola to the Engineer. Maybe it is was unexpected that it would transform other creatures.