I used to not use facebook because I hated people.
Now I don't use facebook because I don't want my E-mail address put on a list that is then sold to the highest bidding spambots. Because if I want to keep in touch with my friends, I will call them, or text them, or preserve the decaying mail system and send them a letter, or write an email, or, heaven forbid, possibly even walk up to them, face to face, and say "how's it going?". Because facebook qualifies as freaking MALWARE. Because not having a facebook with drunken posts and dubious pictures is one less strike against me during the periodical internet background checks. Because I don't want anything put on my computer that proceeds to mine my personal information, which is then sold to the marketing divisions of large corporations OR WORSE.
/rant