Why use the Goo? and not Facehuggers?

Well you see if my idea was spot on or close and reflects the clues in Spaights Original Draft then the Goo would be the PERFECT WEAPON to use to RESET Life on Earth. If we consider the effects of the Goo at the start of the movie and the effects of the Scarab at the start in Spaights Draft. Then why create the Xeno, or why re-weaponize it, the perfect Weapon is what we saw that the Engineer drank. Basically drop a shed load of that on Earth and it would mutate many of us and break down the DNA of others into new lifeforms that contain same DNA that we already have. If Mankind has become selfish, powerful and advanced and does not see the Engineers as Gods no more, then Humans mutated by the Goo or dissolved would reset us back to the start of our Evolution it would change us into mammal based Organisms and Hybrids that would then surely lose its knowledge it once had and become primitive again. Engineers could come down to Earth to visit these primitives again when we would be less of a threat. As if the Bio Weapons effects are same as that in the Urns then all it does is create Organisms based on Xeno DNA that are deadly and hostile as opposed to what the Substance at the start of the movie did with the Engineer. This is why the Original Draft Scarabs effect made more sense and links to how i interpreted the Movies Goo. The Xeno could had been a experiment created with the Goo just as Mankind was via using Goo with Engineer, maybe they used the Goo with something else and it produced the Xeno type Organisms and Goo, or maybe the stuff in the Urns was produced from the Xeno by infecting it with the Goo. But the Weyland File seems to not support any of that, basically here is what Weyland found out about the Goo. The substance in large amounts taken orally will break down the victim at a molecular level and the matter they then break down into contains their DNA which when it contacts another life form will merge with that life form and create a hybrid that contains the Organism DNA that was effected by the Goo. Well not quite as it actually just says the subjects DNA is broken down, and the time it takes to do is depends on amount ingested. The other effect is inhale which will confuse and result in memory loss to the Victim and then it would end up having a primal instinct and become violent it then starts to mutate before eventually breaking down also. By inhale i assume they mean if the Goo comes into contact with the Organisms body.

"..Basically drop a shed load of that on Earth and it would mutate many of us and break down the DNA of others into new lifeforms that contain same DNA that we already have..." What happens to our story when the mutation takes place and results in no human shape ? From what we have seen any meeting of goo and human results in a non human shape. We accept Engineers and their Earth's history because there is a similar design..2 arms, two legs, head and similar body proportions, I guess it is possible that such a mutant shape might be less severe...but if the use of goo created a more adaptive smart species that the Engineers could exploit then the human race that we know would disappear. Big Dave thanks for your detailed post. Not only good ideas, thoughts but explained in a way that I hope I can understand.

TRansforming humanity,,Even if we accept this noble reason for The Engineers,,why at such an extreme part of the universe. Why Earth of all places? This must be a thread somewhere. But why were the Engineers so active and persistant in first seeding earth and then transform the humans and other life forms on land and in the sea?

Yeah i am not saying that dropping the Goo the Engineer had taken would change us into well different versions of us, the change would maintain our DNA to a degree but then the outcome could be different i,e maybe as close as a Ape is to a Man or as far as a Cow is to a Cat etc. Also there is no saying that the Cargo on the Juggernaut contains the same as what was in the Mural Room. Well not from the movie.... But the Weyland Viral File does suggest that the stuff the Engineer drank and what Holloway had was the same thing, and so maybe when mixed with the outer slime.substance it produces the reaction we see that leaked from the Urns that the Worms was swimming in and Fifield fell into.

Maybe they tried seeding a different planet, and when the dna mixed and they came back, the xenomorphs were alive. The Engineers could've created loads of different life on different planets through goo experimentation .