I'm not an over educated DUmmie, but a "study" looking at "homicides" at the state and county levels does not seem to matter when it comes to justifiable homicide as it applies to SYG and Castle Doctrine laws. "Homicide" is a pretty broad category.
As for the FBI statistics dropping, seems to me that one major factor is the recent citizen friendly laws that no longer punish people for defending themselves. Considering almost every release of crime statistics shows a sharp, downward bend in numbers where concealed carry laws have been relaxed, I would tend to believe that the leftist study cited in the DUmmie's OP is created bullshit.
DUmmies, you need to pay attention to what I am about to say: Anytime someone cites a study, for or against anything, ask them exactly what the raw data showed and how the conclusions were reached. Any organization with an agenda can manipulate or outright omit whatever data they wish to prove their point; a good example of this would be the Hockey Stick Graph. Unless you can look at the raw data and extrapolate a real, scientific conclusion, you're just parroting someone else's analysis and, more often than not, spreading propaganda.