Unless we're going to believe that the self-selecting YouTube questioners were utterly different from the rest of American voters, it seems pretty clear that CNN ignored these complex -- and highly relevant concerns -- for an issue that served its ratings interests -- immigration -- or ones that made for moments of conventional television conflict, like gun control, which doesn't even show up in surveys of voters' concerns.
Well, why the hell wouldn't we think that "the self-selecting YouTube questioners were utterly different from the rest of American voters?" As I wrote on Friday, it's actually amazing to believe that any regular American voter would shoot, edit, and upload a question for a YouTube debate. How many people were aware and motivated enough to even watch the debate? About 1.5% of us (4.5 million people watched). How many people like to shoot and upload videos of themselves to YouTube? VERY few. So it's actually perfectly reasonable to assume that most of the questions submitted would be from partisan activists with an agenda to push and not representative of what most people think.
As I discovered over and over again at Spinsanity and in my life working in the media, it's always easy to throw around accusations of bias, but there are usually much more system reasons for journalistic faults (real or perceived).