I’m closing out 2012 on an unusually positive note. As I explained at length in my column Sunday, I see it as a year of tipping points, in which America made decisions on contentious issues — gay marriage, marijuana, taxes, government, immigration, Obama. Not that everyone agrees or that everything is solved, but I’m upbeat about 2013 and the years to come. Maybe it’s partly personal, reflecting confidence in my children and their young adult peers. In any event, I welcome your thoughts on the tipping point thesis. And I thank all readers and contributors joining in the conversation in the year ending and the year to come.