I've never been in a fandom where 'aliens made them do x' was a big thing. In HP you'd get the odd magical marriage malarky, but it was by no means full blown 'aliens made them do x'. Recently I've been reading ST XI and SGA stories, and this trope apparently went through the fandoms like wildfire, because man, it is everywhere.
So what's it all about?
Near as I can tell, the appeal is some outside force pushing the characters into doing something they otherwise would not do (but sometimes secretly want to), for angst, lolz, and sexytimes. It's not hard to understand why that would be fun for writers and readers alike. You, the writer, get to force the characters to do something OOC through the actions of another character, and the hand of god has legitimate story camouflage. Then you get to mine the situation for character development, fun, and emoporn. Additional thrills are garnered from the wacky customs of the aliens themselves. There's a kind of fantastical exoticism going on here, where alien customs are inexplicable and hilarious, and the aliens themselves are ignorant of Starfleet/Earth customs, and stubbornly cling to their own ways. And not only that, they force outsiders to conform as well!
The more a story leans on 'those wacky natives,' the skeevier it is. I much prefer stories where Starfleet officers are performing a new and unfamiliar ritual, in order to honor allies that they respect. Or if you want to retain the element of coercion, stories where characters act OOC because they've been exposed to mind/body chemistry altering substances (and not by the aliens!). I don't know, the more 'aliens made them do x' stories I read, the more uncomfortable I am with them. There are just so very many of them that revel in things like describing the strange costumes, dwellings, foods, and rituals of aliens. They live in huts, how twee! And describing in even greater detail how put upon our heroes are, victimized by primitive, stubborn, unfeeling (or alternately too emotional) aliens. By and large, the aliens' actions are irrational, often opaque, and the aliens themselves are rarely fully realized characters. I'm not saying that all these stories are bad - far from it - but... some of them are just so goddamn creepy, and it's the ones that don't intend to be creepy, that are the worst of the bunch. Oops, I just happened
to use a handful of colonial stereotypes of Darkest Africa
to characterize my aliens. But the aliens are ~noble and well-meaning, so it's ok. Seriously?
Anyway, I'm looking for some good meta that examines the trope. Links, anybody?
Oh, and if you've got non-creepy fic recs, I'll take those too. ;)