Right after 09/11 I did a flight to Washington, DC, and turned around back to the west coast Nobody was on the radio; the skies were mostly empty. We were contacted three times on the way out and advised we were being intercepted.
On the way west, some clown took off in a light airplane and got intercepted and escorted down. I can't possibly imagine he was the only person in the country who wasn't aware of what was going on, so the only explanation can either be wanton disregard, or raging stupidity.