I think the main problem with using Facebook comments is not so much that they assume you have one identity, it's that they don't allow you to isolate things be

I think the main problem with using Facebook comments is not so much that they assume you have one identity, it's that they don't allow you to isolate things between websites. I comment on a lot of websites, the internet is my home, I don't mind people reading my comments on another website, if my parents saw my hackernews comments it wouldn't be of concern to me, however if all my hackernews comments were pushed to my Facebook feed and every friend on Facebook saw every comment I leave that would be a problem because it means I would have to consider them as an audience too when commenting. Context is important, most people on Hackernews have the same background (technology) and will approach the comments others write in a similar frame of mind, however my parents would understand what I say in a different way and it would mean I'd have to consider the meaning of my comments to everyone, it would change the dynamic. I think it's more about context than it is "personality" or having multiple personalities. In some ways they're the same thing though.