I'd class myself as a Romney tax returns agnostic. I don't have a clear sense of what's in there or whether there's anything in there. But this is a very odd explanation. He seems to be saying that his Republican supporters are under the impression if he just releases all his tax returns the whole issue will go away. But he's saying, quite the contrary, my friends!
He says that's because Democrats have become much meaner than they were in the old days. But that doesn't sound very convincing. He seems to be saying more or less openly that if he releases his tax returns it will only get worse.