Really kind'a does. The Deacon needed an infected human male to inseminate a human female who then gave birth to a squid-hugger-thing which then impregnated an Engineer. That's a ridiculously convoluted, not to mention awfully precise, sequence of events that needed to happen -- and considering the only consistent thing about the black goo in the movie is that its reactions with individuals are inconsistent, the movie basically shows (intentionally or not) that even if you did recreate those circumstances, you'd get different results anyway.