To be clear: They are a threat, the magnitude of the threat and the correct military response is unknown. I work at MIT/lincoln Lab these days. One group I worked with (I was not involved) did a test where they had 25 drones and 12 low power networked distributed radars. They collected the data and did the data processing offline. The offline results showed they could track all 25 with sufficient power to counter ( shoot down) all the drones. When I was at BAE the group I worked with (again I was not involved) had a ballistic system (a gun) that could shoot down drones with one shot every time, though the test was basically just skeet shooting, the drones flew in a narrow corridor but the gun had to be fast and accurate. The same group demonstrated a Bradley fighting vehicle that could shoot down RPG’s a few years before, but that’s all it could do, defend itself against RPGs. The Army did not find it worthwhile.
During World War II the SCR-584 could shoot down V-1 flying bombs that came within range. The V-1 was an early model drone. The Germans and Americans both used radio guided air launched missiles during the war with limited success.
BTW, the skeet shooter had a laser version but they were not allowed to demonstrate it because of flight safety, the hazard was to the sight of aircraft flying withing 25 miles.