And also a huge waste of energy on an ongoing basis. An aircraft has to continuously expend energy on fighting the gravity.
> the problem with digging is that many people live and work and drive right above where you dig.
The FAQ addresses that by noting that below ~2 tunnels height, people wouldn't even notice.
Easier, yes. Cheaper, no.
> At some point the holes could cause collapses.
The risk is extremely low, and car accidents have caused a vastly greater number of deaths than any other form of transportation.
> There's also water mains and other hazards and obstacles.
Pretty sure there were some pretty massive hazards with flying too.
> Sounds dangerous.
Which a lot of people said about flying as well. And it's vastly safer than a car.