This difference has nothing to do with real names or anonymity. It has to do with the fact that your FB friends have something to lose in that context: namely, their personal connections to mutual friends.
So, do you think they would have anything to lose by posting the same comments elsewhere using their real names? Personally, I am less likely to comment if my real name (coupled with a real-life social profile) is attached to the comment, whether or not I am posting directly on the social network my name is attached to.
But the effect on Facebook is generally to imagine this: all of your contacts are in a room, and every time you comment, you're getting up on stage and saying something. No catcalling from the audience. You're walking all the way to the raised floor and taking the mike and looking out into that sea of people like James who saw you naked in high school during that pool party and Gina who still believes that we should have committed more troops to Iraq and Joe who doesn't really care about anything other than free beer, though if you ever bring up the mutual coworker he dated, he'll rip you a new one.
It's this complete cacophony of context--context that matters, that's important to you--and it's not actually possible to manage it as is.
Do people post about Important Issues and Discuss Things Maturely and Deeply on Facebook? Of course they do. They do it everywhere. They do it face to face. They do it on the phone. They do it on national TV. They do it over email. They do it on Twitter. They probably do it on Snapchat, but I don't pay enough attention to notice.
What's the trick to getting that kind of conversation on Facebook? Same as any other place. Would you talk about your intimacy with James while Joe's around? Unlikely. But if you went and got a coffee. Or if you started a Facebook Group of some kind, or a private message, or whatever: anything to limit the contexts that invade into a conversation. (Alternately, there are actually super-public spaces on Facebook that get into reddit-style arguments.)
Anonymity, of course, does this automatically, because context is attached to some identity. But that doesn't mean anonymity is the actual mechanism. It's the hand holding the hammer, not the hammer itself.
At the end of the day, anonymity doesn't actually do anything.
>>>> Personally, I am less likely to comment if my real name (coupled with a real-life social profile) is attached to the comment.
This is the very reason I have no social media accounts that use my real name. And many people on my FB feed, have no idea what my Twitter handle is and vice versa.
It's a great feeling to have a completely unencumbered sounding board where you can spew whatever you want (within reason of course) and your friends, co-workers, current or future company employing you will never know.
Recruiters and companies always ask for my social media user names and I never tell them. It's nice to know with great certainty they won't ever find them unless I give them up willing.
I think there is a difference, yes. The Facebook status stream is very in-your-face. When you say something on Facebook, you're pushing it to the eyeballs of many people in your actual social circle.
If you say something on a forum where, say, you are linked to your Facebook profile, you're not pushing that comment to the eyeballs of everyone you know. My online social network is now essentially the same as my offline social network, and there's not too much that I'm okay pushing to the eyeballs of everyone I know. Not because I'm ashamed, but out of general courtesy.
I post on Reddit, and I use my real name as my account there (same as here). I comment much more freely there, because a) I'm less likely to actually run into someone I know, and b) there is a wider variety of topics being discussed there.
I've seen people send rape and death threats to people _from their work email account_, so yes, often anonymity isn't strictly needed for people to be terrible.
