I don’t see how anyone could reasonably take this comment, taken in context, as a call to violence.
I don’t care for this kind of rhetoric (actually I was one of the members of this forum calling for greater civility in our discourse all the way back in 2004), but I certainly didn’t care for Sarah Palin's “Don’t retreat, reload!” either. I can’t see it as anything other than completely hypocritical to act outraged at this remark while defending “Don’t retreat, reload!”
I am, in any case, more bothered by the faux outrage that springs from these kinds of comments than the comments themselves. I think there is, and needs to be, room for irreverence in public expression, and as a nation our sense of humor and tolerance for expression seems to be atrophying. I can’t imagine, say, Reagan (much less Teddy Roosevelt) whining about this kind of thing.