And the $50 drone has a payload of about 2.2 pounds(or one kilogram). That is easily a hand grenade, actually four hand grenades. It would be more likely a EID like hand grenade, that could kill between one and twenty people. The EID might not be a combination between a hand grenade and a claymore. It would destroy the drone in the process, but even for an insurgent operation could afford that.
We are getting to the point with off the shelf parts, and open source software, you could have such a drone flying itself, and coordinating with other drones. For the $10k a government might buy one drone with, a relatively small operation could buy a fleet of 200 drones that could attack any crowd out in the open.
A truck bomb needs to be delivered. So lets say you want to get it into Manhattan, you have to get it through a tunnel or a bridge, and then into the exact area that you want to hit. All along, they are taking pictures of you.
Then it is a very centralized bombing. There is a reason many times weapons designers use cluster bombs. It spreads out the carnage. Smart drones working in concert would really spread out the carnage very accurately.
Imagine releasing 200 smart drones, 50 miles away. It is something that could actually be gotten away with... Maybe.
Or maybe not. I am speaking in terms of possible futures, not definite futures. I know there are people working on open source projects like this, but do not know how far they have gone. I certainly hope this is not the future.
Now that is completely true. Terrorists are nowhere near as dangerous as just normal cars.