For everyone else's edification, I will try to get us back on track by tying this back to Eberron and why MGuy underestimates the squick factor on breed leeches.
Next: you've repeatedly steered this conversation towards details about the mechanics of facehuggers and away from the actual point which is about themes and content that are or are not acceptable to various audiences. I called Alien a "monster rape movie," which may have been sloppy. I should have said: Alien is a monster movie. It is also a rape movie. The relationship between those things is a little complicated.
For instance: Let's concede for the sake of the argument that there exists a defensible notion of "rape" such that there is no actual rape onscreen in Alien. That's fine for my position because a movie can be about [skub] even if it does not have any [skub] in it. The Crucible is a play about red panic that does not have any communists in it. The Book of Daniel is a book about King Antiochus Epiphanes, in which King Antiochus Epiphanes is not a character. And Alien is a movie about rape.
I want to give you credit where it's due, so let me acknowledge: yes, parasitism and rape are different. Rape is an essentially human threat. (other animals have forced sex within their species, but they don't go around raping humans). Having parasites in your body is bad enough to cause body horror for many people, but botflies aren't menacing because they're impersonal, unintelligent. To get an effective rape metaphor you need to add an element of human malice.
The thing is, Alien does that. The facehugger isn't necessarily the rapist in this story: Ash and Weyland-Yutani are. They want to retrieve the alien, and they're willing to risk and to use the crews lives and bodies to get what they want. That's the dynamic that clinches the film as a rape metaphor. If you look at it as a parasite movie, you miss the point of Ash's entire subplot.
What Breed Leeches actually do is arguably less invasive and traumatic, than that, sure. It's "just a bite on the arm," it doesn't seem to do much to the primary victim, and it just changes a baby that already existed. But that's the problem: breed leeches, unlike vampires, attack actual pregnant women with big bellies and everything and their demon-children actually have to get delivered in a conventional childbirth. That's way more upsetting to think about than some dude punching his way out of a coffin. Anything to do with pregnancy is an emotional lightning rod for many people (especially many women I have known), and I think having a foreign infection alter your fetus is upsetting because it feels like a plausible threat.