Moving social stuff into the browser should actually help make it more open. If a page/framework uses this Social API instead of hardcoding against a few popular networks, it opens the door for you to choose how the integration works.
Hundreds of millions of folk use their browser for social stuff. It's not an unreasonable use of developer time to make the web better for those people. (It probably springs from their work on FirefoxOS in any case.)
The small set of folk like you can just disable it. (Or, as is pointed out elsewhere, just never enable it in the first place!)
Yes, I'll probably turn it off. And then when they add some strange mapping API, I'll turn that off too, and then finally when they add a storage API I'll switch to a browser that isn't trying to be everything to everyone.
Until it gets accidentally turned on by a browser update, or by some rogue plugin (wouldn't put it past Adobe actually), or by an optional Windows Update, or by some grayware that I mindlessly install on a computer.
If it's off by default, it should be in a plugin. If you want it, come and get it.
