Your last question is hilarious.
If someone is insane, there is no rationality to their violence. James Holmes had some kind of Batman fixation.
How does that relate to your favorite four facile excuses (see my "launch" reply above)? 
The Virginia church shooter did so out of racism.
The Texas church shooter had a history of domestic violence against his wife's family, and apparently shot everyone in the church out of animus towards the wife's family.
The guy who shot up the gay bar in Orlando obviously was not pro-gay.
How do those shootings relate to your favorite four facile excuses?