The thing about Real ID is they're treating it like this huge step forward. You'll be able to talk to your friends across multiple games! But they very pointedly state that it's for your REAL life friends.
In the days before Warcraft 3, you could already talk to all your friends playing battle.net games no matter what game they were playing. This is a step back from that, where, if you want to talk cross game with someone, you share a lot of info with them.
You give them your full real name, and email address.
You give them access to you on ALL of your game accounts across all current Blizzard games.
You give them access to your ENTIRE friends list.
As it stands right now, you can't turn any of this on or off. At Blizzcon 2009, they said that with such a powerful feature with so much information, they'd have plenty of knobs and dials for privacy and parental controls. But the only privacy option currently apparent in Starcraft 2 is that if you don't want people to know every last detail about you, don't add them as a real id friend.
I can respect that Blizzard wants to make a neat system for you to have easy access to your real friends with, that's cool. But it's just such a failing on so many levels that you have to give up all semblance of privacy for cross game chat - something we had a decade ago - without any of the flexibility they promised us.