For as long as we’ve had the Internet in our homes, critics have bemoaned the demise of shared national experiences, like moon landings and “Who Shot J.R.” cliff hangers — the folkloric American living room, all of us signing off in unison with Walter Cronkite, shattered into a million isolation booths. But watch a live mass-media event with Twitter open on your laptop and you’ll see that the futurists had it wrong. We still have national events, but now when we have them, we’re actually having a genuine, public conversation with a group that extends far beyond our nuclear family and our next-door neighbors. Some of that conversation is juvenile, of course, just as it was in our living room when we heckled Richard Nixon’s Checkers speech. But some of it is moving, witty, observant, subversive.