> they are inherently fuel inefficient compared to devices with wheels assuming it can be harvested cleanly, energy isn't inherently a problem until we start g

> they are inherently fuel inefficient compared to devices with wheels assuming it can be harvested cleanly, energy isn't inherently a problem until we start getting close to capturing a significant fraction of total solar irradiance. we get better at this every year, so eventually it will be a non-issue. > they are noisy, a problem which can probably never be solved unless breakthroughs are made in science-fiction fields like anti-gravity imo, this is probably the biggest obstacle. like you say, there's really no plausible breakthrough that could reduce the noise level to something that could be acceptable in a dense environment. > airspace is very limited. In my country, we have already serious planning problems with the current amount of air traffic idk what country you live it, but this is probably only true at higher altitudes and in the immediate surroundings of airports. > airspace is very limited. In my country, we have already serious planning problems with the current amount of air traffic this is important, but people won't necessarily care. the other items in your list would probably delay adoption but not prevent it altogether.