I think it is a given that this, and others that commit similar crimes, have to have some level of derangement. I fully agree that this man is fully responsible for his actions.
On a larger scale I think that his actions are symptomatic of the increasingly heated divide in America. One that is growing in width and vitriol.
Such is the style of modern politics, wedge politics, championed by the american right. I could tee off on this but at 5:30am I haven't got the energy left. Maybe some other time.