“How is a flash suppressor a threat?” The Federal AWB was all about cosmetics, and a flash hider was one of them. I think Feinsten’s goal was to have a readily-recognized visual she could use for conditioning the public.
During the Clinton AWB there were over a million ARs sold sans hider or bayonet lug and the antis seemed to be fine with that.
Run! He’s holding a flash hider!
IIRC, there were many rifles sold during that period that had permanently affixed (pinned or high-temp silver soldered) muzzle brakes. Apparently an easily-accessible *threaded muzzle* was also of great concern to the political left. Probably lingering misconceptions about silencers was driving that. Funny, now you can get anything down to a bolt-action .22 with a threaded muzzle. That must be one of those "unintended consequences".