Any theories as to why FB won't allow advertisers to combine KWD combinations so they can be used as a double filter using the AND operator instead of OR? (Ex: Twilight AND Collecting Action Figures)
There's been many times where these combos would really come in handy for targeting.
You can make different ad set to accomplish this. Correct me if i am wrong.
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I am a total noob so sorry for the stupid question... 
But how do you do this?
Do you need the Power Editor to do it? I feel a little bit stupid right now. :P
Don't think you can right now.
You can of course make different ads and ad sets with alternative targeting to get the 'OR' functionality. But it is not possible to force targeting to users that overlap between several precise interests. (e.g. the overlap in a Venn diagram). It would be great if you could!
However, when using broad categories you can target people who like all the selected categories or any of them.

It's like no one actually read my post...
I understand it's not possible. I'm just looking for theories as to why FB won't allow this as the crossover is both completely viable for FB and useful for the advertiser.
No idea - perhaps they will in the future. It is definitely a great idea for very precise targeting. You would certainly want to limit it to only two interests.
However you can likely achieve something similar using Graph Search and building an audience list, though it is a bit more annoying and the audience won't be as large.