The Human weapon

Hey all, here's my silly little theory of maybe Mr Scott and co's thinking. The movie plays off in 2093 and 2000yrs prior to that apparently the Engineers were planning to annihilate us human's by what we think would have been a biological weapon. Now reading all these interesting theories of everyone here, it still buggs me that if LV223 is suppose to be a weapon engineering facility or planet where biological tests are done, why create a biological weapon and not physical weapons to destroy their "enemies" (us). So maybe, we weren't on their list to be destroyed but rather to be transformed/mutated into becoming the Xeno's or an altered soldier. Everything ive seen of the "black goo" is that whatever it creates, that creation is violent. Shaw created a squid like baby, and Charlie along with Fifield became mindless "soldiers" out to kill. So maybe, the Engineers were fighting amongst themselves (cival war), or fighting the Ananukhi or some other alien race and needed the soldiers (us humans) to fight for them because of dwindled numbers. Their plans were either halted 2000yrs ago because of war or they were exiled and pushed out to these planets where the last remaining number of them started to develop biological weapons. Just a thought!