Can we effectively prevent bad actors from acquiring them without too much cost to everyone else? (plus how bad is it if bad actors acquire them) For some things the answer is yes : rockets, missiles etc... For others no: slingshots, skateboards, lawnmowers, scooters, remote control cars etc....
Drones are too easy to build to effectively prevent bad actors from acquiring them without a huge cost to society as a whole. Restricting all the components you'd need to prevent a terrorist from building their own drone is just too disruptive.
Less restrictive regulations like requiring licensing may be effective for other purposes, but not for preventing drone terrorism.
given that fireworks and powder are easily available (re: Tsarnaevs) or relative availability of ANFO (re: McVeigh) and similar stuff or that just one visit to Home Depot allows you to buy components making for a pretty good explosive, i think the explosives are regulated mostly to avoid them lying freely around under the kitchen sinks and in the garages and to avoid being handled by clueless people, not to protect from terrorists.
It also gets you a visit from the feds. Those sorts of purchases are tracked very closely since Mcveigh.
I bought acetone, hydrogen peroxide (in the form of a wood bleaching kit), and hydrochloric acid together in 2002 at a Home Depot and never got the slightest bit of attention.
I also bought an 80 pound sack of ammonium nitrate from a fertilizer dealer in 2002 with cash. I didn't show ID. The employees didn't grill me at all. I was pretty surprised, actually. I thought there would be some sort of tracking in place six years after the OKC bombing and 1 year after the 9/11 attacks. Maybe they only start tracking when you try to buy it by the tonne. Maybe my appearance (clean shaven white guy with glasses, no tattoos) gave me a pass where other sorts of buyers might need to show ID or explain why they're buying.
https://www.businessinsider.com/oklahoma-city-bombing-ammoni...
" the new legislation will require anyone buying more than 25 pounds to register, be screened against a known terrorist list, and require any thefts to be reported within 24 hours. "
Ditto for bulk sugar.
If I think along those lines, the drone attacks are using drones as the delivery mechanism for the explosives, and whatever they are using for detonation mechanism is not interesting here. The explosives are regulated. So should the delivery mechanism be regulated? I think yes-- other delivery mechanisms for explosives to a target are guns, cannons, rockets... all regulated.