Movie Poison: "Splice"

I'm at a loss to describe the level of poor writing squick that ruins the last twenty minutes or so of what is otherwise is a very serviceable and tidy horror movie. Suffice it to say that I've read enough terrible fanfic to know badfic when I see it and "Splice" unfortunately shifts from something an intelligent 25-year-old has written to something that's more appropriate to a fanfic.net R-rated sexual freak-out written by a socially maladjusted 15-year-old. This was incredibly disappointing, because the rest of the film is actually rather good. I like horror movies that are a long, tension-filled exercise in waiting for the other shoe to drop, and "Splice" was this in spades. Two scientists, both too arrogant for their own good, create creepy-looking worm-like creatures in order to replicate proteins, drive the plot, serve the evil company they work for, etc. What's next? Create a human-thing creature, naturally! As I said, the plot is a long wait for something bad to happen as a result of a lot of incredibly poor/arrogant choices on their parts (of course with the noblest of intentions). I'm sure there are a million problems with the "science" in this movie (not the least of which is along the lines of WHY?!), but it's presented in a fairly convincing way. It quickly becomes obvious that the motives in creating a human-hybrid monsters are incredibly poor; one of our heroes wants to have a baby without the inconvenience of getting pregnant, while the other craves the God-like treatment he thinks they'll inevitably receive from the scientific community. The creature itself is convincingly creepy at all stages of its development. Its final, adult incarnation is chillingly played by Delphine Chanaec, who manages to portray something that can mimic human emotion but not understand it, and only use it as a means to an end. And, as I said, the first 3/4 of this movie is very good, with the tension slowly building. (There's also an unintentionally funny sequence that's very reminiscent of the moment in "King Kong" when the first public display of Kong goes horribly wrong.) But the last twenty minutes... how the mighty fall. All semblance of the bigger thematic plot goes AWOL, and befuddled chasing through the woods and a truly disturbing sexual/linguistic thing happens. Why, movie, why? The only thing I can think of is that the writers realized they'd painted themselves into a corner and didn't want some kind of happy, compromising ending. But, surely, there are better ways to get out of a plot corner than this! Well. Rent this with your bioscience-minded friends to make fun of, and cringe at the badfic ending. Or simply skip the last twenty minutes.