"What exactly separates a “terrorist” from a run-of-the-mill mass shooter? Are these just political labels we slap on when we want to funnel more money in one direction or the other?"
I say, yes, they're just political labels slapped on to justify gov't spending and powers. Instead of trying to stop people from murdering for rightwing causes, leftwing causes, armed robbery causes, religious extremism causes, the insurance money, spousal abuse, we should just be enforcing the laws against murder.