By contrast, here's Casten's post at Grist, and I have no idea how to make sense of it. He appears to believe that the dividend part of cap-and-dividend would somehow allow people to purchase their way above the cap, and that the price penalty given to high carbon sources wouldn't help renewable energy producers. And in the comments, he "clarifies" that the same arguments don't apply to cap-and-trade.
I don't get it. Even more confusingly, he's apparently worked in renewable energy, so he's not some random guy spouting nonsense.
Matt Yglesias critiques him here. As I wrote in the comments, the uncertainty over the extent of reductions applies to a carbon tax, but not to any cap proposal. David Roberts appears in several places to defend Casten, but never tries to explain what Casten is actually saying.
And in case it needs clarifying, I still think the 100% cap-and-dividend proposals are politically unrealistic, that the Waxman-Markey bill is very good, and that I'm waiting to see what's in Kerry-Lieberman.