The problem is that flights are not sustainable much longer. Flying uses an astounding amount of subsidized fossil fuels, requires infrastructure that takes up quite a large amount of space, and is increasingly both inconvenient and intrusive. They're also a separate matter from the last-mile problem that bicycles, scooters, and autonomous vehicles aim to solve (assuming we can structure AV use in a way that, during the transition period towards full subscription use, doesn't increase traffic like so-called ridesharing taxis do now).

The United States can be one of these countries funding HSR. Countries that are quite pleasant to live in--and some that aren't, depending on your outlook--are already funding HSR and already have expansive rail networks. There's no reason we can't, too.