HELP ME MAKE SENSE OF PROMETHEUS!!!!(SPOILERS)

After seeing Prometheus I am highly disapointed. I am a huge fan of the Alien saga. There are wayyy too many pit falls and condradictions and sadly I feel that Ridley only came back for a pay check.I feel he spent more time trying to dissociate Alien from the film when he should of been associating it. The last minute apperance of that reptile like creature seemed to be a far cry attempt to draw fans of Alien into seeing Prometheus 2. I also think the Blame lies with Damon Lindelof who was the executive producer and writer.Lindelof is also responsible for LOST which in all honesty was a Train wreck of an ending.So why let him near such a beloved saga? [b]Firstly . . . David . . [/b] David is a robot,one of the 3 codes of robotics is that they cannot hurt human beings in anyway.the promotional videos with David in them for the film(http://www.youtube.com/watch?v=3oU-yT4nfkY&feature=fvwrel) clearly show David saying that he is aware of human emotions just cannot feel them. surely the act of deliberatedly infecting someone defies the laws of robotics that are enforced in the promotional videos. Why does david even bother infecting charlie(shaws boyfriend). What is the reasoning? even this defies the laws of robotics as maliciousness and deviousness are human feelings. I considered the fact that perhaps it would be to see if charlie became immortal testing it out before applying the method to peter weyland but even this defies the laws. [b]Secondaly . . Black Goo[/b] If the black Goo is a biological weapon then why did the enginner at the very start of the film deliberatedly drink the black goo?.And also if the goo had the effect on the enginner and Human and enginner DNA are supposedly Identical then why didnt the humans disintegrate and decompose like the enginner? Where did the black Goo even come from?? Where did the reptile creatures in the tomb chamber come from?? The movie implys that the tomb was a military base and the engineers devolped the black goo.But why?It is also implyed it was developed to destroy the humans.again . . . why? Why would the enginners create human life to destroy them?Is it simply just because they can ? or like David suggests in the film perhaps humans were becoming too far evolved and threatened to over power the enginners . . . but even this does not make sense as the film at the begininng states that if the engineers are real then evolution cannot be . . [b]Finally . . . Final Alien creature[/b] The creature arises as a result of the octopus creature overpowering the enginner. why does it resemble an octopus ? and was it a result of the maggots in the black Goo? Is the Black Goo like a DNA transcribing Mechanism that isolates the worst parts of the DNA and exploits it into vile creatures? The fact that the full grown alien emerged from the enginner could it be a possibilty that the enginners are only shells for the aliens the whole time,Like Cacoons.and the black Goo acts as a catalyst to release the alien? Why does the alien look reptillian and not like our traditional alien?? the only answer I can assume is evolution of the species . . . the same evolution thats disproved by the crew by finding the enginners!! Unfortunately Prometheus is too vague a film for any interpatation to be correct.I completely agree with writing that leaves the audience to decide the faith of a story but not when key elements are neglected and random occurence events are incorporated to simply attempt to be creative story writing. In conclusion the film is insulting to the Alien saga in my opinion and its attempt at complex story telling yet again left audiences LOST