I've seen you post this comment 3 times. I'm going to extend you the courtesy of assuming you're not a troll.
Let's assume the FBI knew this guy was intending to fly a gryocopter into no-fly space. Let's further assume based on reading this guy's emails,or tapping this guy's phone, or rummaging through his trash, or his refrigerator, or installing secret spy devices in his underpants to measure his potential for Communist sympathies, that they decided he's a legitimate protestor and not a home-grown terrorist. In that case, shooting him out of the sky risks public out-cry. Particularly since the air-defense systems around DC no-fly zones are SURFACE-TO-AIR MISSILES. Weee bit of overkill there. So what's less headache? Shoot the kook down or let the kook have his fifteen minutes of political-stunt-fame and go about your day?