My reasons for forcing Facebook login is to know more about my user in order to serve the relevant/personalize content. It's a chicken/egg situation... how to get around it?
I would suggest you simply ask the user for the information you need in order to give them something, then offer facebook as a simpler way to give them that.
I mean, if you are getting access to their FB accounts to see what they like, why not put 5 input boxes down the left side with something like "Name your 5 most favourite things" with a submit button.
On the right have something like:
"Or sign in with facebook and save some time!"
If they like what they get with the inputs on the left, they are more likely to give you access to their facebook data to enjoy the experience more.
It's a heavily modified Barnes–Hut for clustering, lot of coding in python... used a lil bit of Levenshtein distance too.. alto is 20% of what I want to achieve but need to know if the concept has audience.