You forgot the oil pipeline.
The causes of this terrorist attack:
Racism.
White entitlement.
Christianity.
Gun ownership.
Cigarette sales.
Global warming.
Clearcutting of forests.
The BP Oil Spill.
George W. Bush.
Sarah Palin.
Tea Partiers.
The failure to embrace undocumented workers.
The failure to reach out to Islam.
Mitch McConnell’s stubbornness.
The NRA.
Accusations of voter fraud.
Birthers.
Keystone Pipeline.
Big Gulp Sodas.
Fracking.
Non-union workplaces and Right to Work states.
Homophobia.
Hostility to Native Americans.
CO2.
Obamacare not being implemented fast enough.