Besides the obvious of being totally deranged, Jim D. Adkisson appears to have chosen this particular church because of their liberal views which included being advocates of gay rights and progressive social work.
"It appears that what brought him to this horrible event was his lack of being able to obtain a job, his frustration over that and his stated hatred of the liberal movement," Owen said at a news conference.
Crooks and Liars goes a bit further in their description of Adkisson:
We will most likely learn more details in time, but the picture that’s developing is one of a typical, uninformed Fox News, Rush Limbaugh, Michael Wiener-Savage fan — an angry white male who has been brainwashed into thinking that everything wrong in America and around the world is the fault of the evil liberals.
I am sure that the above is a very over-simplified view but it does get you thinking because I am sure that it describes more than a few people you know or have met at one time or another. It also shows what can, and often does happen when someone lets that intolerance and hatred get the better of them.
UPDATE 7/28: Crooks and Liars might not have been too far off with their assessment after all. Here is Adkisson's reading list per the Knoxville News Sentinel
Inside the house, officers found "Liberalism is a Mental Health Disorder" by radio talk show host Michael Savage, "Let Freedom Ring" by talk show host Sean Hannity, and "The O'Reilly Factor," by television talk show host Bill O'Reilly.