When will right-wingers stop joking about killing liberals?

Dave Niewert at Orcinus comments on the Knoxville shooting. The Washington Post reported that the shooter "stated that he had targeted the church because of its liberal teachings and his belief that all liberals should be killed."

Right-wingers love to "joke" about mowing down, rounding up, and otherwise "wiping out" all things liberal. It's become a standard feature of conservative-movement rhetoric. And whenever anyone calls them on it, they have a standard response: "Aw, c'mon — it's just a joke!" [...]

This was a violent attack on liberals. It was inspired by years of wingnuts talking about how much they hate liberals and wish they could do something about them. This man did. But watch the people who have been telling these "jokes" run away from any culpability for it.