Where's my single social stream?

Social media moguls like Facebook founder and CEO Mark Zuckerberg talk about uniting mankind through the power of social networking. Back in 2012, Zuckerberg wrote in a letter that accompanied Facebook's IPO paperwork that "Facebook... was built to accomplish a social mission — to make the world more open and connected."
That's a worthy mission, and it's hard to find any who who opposes it. We all want a more open and connected world, don't we?
On a practical level, there are two way