The original Alien is very heavy on the rape metaphors. From the way it’s “conceived” through to how Ash tries to kill Ripley (cramming a rolled up magazine down her throat).
He picked that thread back up in Prometheus with the Shaw thing. The part you forgot there is that she’s supposed to be sterile, so she’s not really “pregnant” through fertilization.
In the original Alien, the alien is just using the guy.
The guy is just a host whose only purpose is transportation and shelter.
Prometheus goes a different direction.
It’s all about DNA. The Engineer at the start of the show takes the goop and he falls apart releasing his DNA into the water of the planet.
David gives the male scientist some of the goop but it is evidently different goop that merges with the male scientist’s DNA. Interesting that the goop could survive the alcohol and human defense mechanisms.
The female scientist then has sex with the infected male scientist and something evil happens. Maybe it’s an allegory for AIDS.
The movie series shows us that a female alien lays eggs and that’s where the baby aliens come from. Humans are just hosts to provide transportation and housing for the baby aliens.
Prometheus is saying that the aliens can be transmitted sexually which is a new twist.
The baby alien didn’t come from an egg that was laid by a queen.
Sexual behavior between a man and a woman produced an alien.