I'm obligated to use Facebook - some of the publishers I work with insist on using it. It's also the primary means of communication with my overseas family.
The real name crackdown doesn't affect me - yes, I write under my real, legal name. I spent a lot of time searching my heart on it, but it's a memorable name, it's not similar to anyone else working in the genres and spheres I work in, and I don't write anything "problematic."
Many of my friends use pen names. This affects my friends. I have some friends who may be thrown off Facebook or forced to use their legal name. And Facebook's answer is: Set up a page.
Okay, that'll be $5 for every single post you want anyone to see - which may be a reason why Facebook is doing this. Pushing professionals into using pages not profiles is a money maker for Facebook - and a money drain for those professionals who, contrary to the popular image of business people, are generally not rich.
I went through this all when G+ was being stupid about real names. They stopped, and now Facebook has started. So, I'm going to go over the people this affects again:
1. Writers, artists, entertainers, and performers who are better known under their stage names or pen names. How many people know Lady Gaga's legal name without looking it up? For these people, being found under their real name would be impossible.
2. Writers of erotica who may not want their family (especially their parents or their children) to know what they write.
3. Members of the LGBT community who are afraid to come out to their boss (remember that it's legal to fire people for being gay or trans in many jurisdictions) or their family; particularly 13-18 year olds. Trans men and women may change their name socially before they do so legally.
4. People who are avoiding an abusive ex or a stalker and may literally be personally endangered if they're found.
Facebook can, of course, enforce any policy they want, but they have to realize that they are going to lose a lot of people over this - and thus the advertising revenue. Which will probably exceed page boost fees they're trying to get out of people. (Yes, I'm that cynical, but Facebook has been very money grabby lately).