Verified Facebook accounts .... because it's difficult that there will be more than one account for person.
That's completely false. There are TONs of people with more than one "verified" account. Not to mention all the "blackhatters" that have boat loads of accounts. Guys that are making a shit ton of money using facebook ads go through a lot of "agency advertising" accounts as well which aren't easy to setup and yet they create new accounts day after day when their others get shut down. Couple months ago I wanted to test something and bought 25 youtube phone verified accounts for $5. I'm sure you could find the same sort of thing for facebook.
Fact is, there's no way to distribute anything "fairly" on the internet as there are always people that can come up with a way to get a lot more than anyone else. Not to mention that not every uses or wants to use facebook (there's threads on the Stellar forum complaining about the use of facebook).
Using FB to distribute is not a good idea for a multitude of reasons: inherently unfair for most (see above), big privacy concerns, use of two centralized corporate authorities to distribute, etc.