1.Your local hobby shop drone will not be able to fly for 20 hours like a fixed wing Scan Eagle. Bad comparison. 2. Modifying drones to be used for combat is cheap if you don't count the labor cost, and in relative peace time counting the labor costs and overall cost of fielding a system is fair. If you take a $5,000 consumer drone and want it to *reliably* explode on someone, at small volumes that will likely take enough labor time to verify, let alone certify, that it pushes the price up to closer to the price of the new dedicated loitering munitions...
We can't orchestrate our society around what someone "could" do
You could kill me with a rock easier than you could kill me with a drone
When I get on a bus with other people, I can, with a fairly high degree of certainty, rest assured that the other passengers will not just randomly kill me to get something from me. That's because the people, just like me, have some level of comfort and their basic needs being met.
The further we slide away from that, the higher the risk for everyone. And to maintain that needs constant work, from everyone.
Norms and morals apply almost equally to murder by drone versus e.g. poisoning someone. The difference is largely in deterrence, i.e. having a clearly-communicated capability to find anyone who tries to pull this off.
How about dropping a rock from a drone so it isn't up close and personal.
The difficulty for an attacker is the explosive payload, not the delivery mechanism. If it were easy for an attacker to get an explosive payload there would be car bombs going off every day as an easier delivery mechanism than use of quadcopters.
Thankfully it seems to be relatively easy to prevent people from making explosives, at least outside of warzones in countries with strict border control, because random people don't have a valid reason to buy industrial chemicals or equipment, and especially not chemicals identified as precursors for making explosive compounds. And for plants where such industrial chemicals are legitimately necessary to use, inputs and outputs can be measured, and detection taggants[1] used, and many other security measures, to prevent accidental or deliberate loss of control over such chemicals.
[1] https://en.wikipedia.org/wiki/Taggant#Explosive_taggants
I don't think there's a solution. I've worked on projects in the USA trying to predict behavior changes in veterans that lead to murder/suicide and it's just not possible.
Just try to avoid people that have been in warfare - don't hire them, don't date them, they're broken and can't be fixed.
I do think that war would be better off being done remotely via automated floating and aerial weapons platforms controlled remotely if not semi-autonomously. I mean without soldiers on the front line.