It's an important question, how we came to this pass.
I suspect, and here Lehrer will not agree, that responsible, staid journalism like his, as practiced in America, is part of the problem. The attempt at "balance" requires some definition of the scope of acceptable opinion. As Eli taught me, the implicit limits of discourse, which oddly include Singer and exclude Lovelock, for instance, is called the Overton WIndow in some circles.
Here's an easy place to start. As Gore suggests, don't give equal time to sense and nonsense.
If the window of acceptable opinion doesn't move with the evidence, journalists aren't doing their job of presenting evidence. If they hold a misguided scruple against making judgments, the window will wander around in ways that don't have much to do with reality. That's when Mamet's principle kicks in, that's why we have lost the capacity to cope collectively, and that's why at this point all genuine optimism in America is centered around the idea of abandoning the collective altogether, which unfortunately won't work.
Jim Lehrer is a very nice man, a very smart man, a very serious man, and a very well-intentioned man. And Jim Lehrer is part of the problem.
Update: The CBC ombudsman is quoted as follows on DeSmog:
"The CBC, in its decision making process, is entitled to make its own editorial determination about what opinions are in the mainstream, and need to be reflected, and what opinions are on the margins, and can be given the editorial hook they so often deserve…"That is pretty much the point. Journalism is not only entitled to make such decisions. It is obligated to do so, and it is obligated to do so responsibly and competently. That is what we pay our journalists for.