Litmus test: if cost was not a factor, wouldn't you prefer to travel via private jet?
Tells me that we're still hurting for better mobility in this world.
Climate wise that cost was amortised from metals consumption by the developed world.
If I'm going to consume vast quantities of resources then I do like to see benefits flow to as many others as possible.
Now that I'm in a rural area I see large quantities of fuel consumed by tractors to put grain into the mouths of millions.
Shorter ones, again, if cost was not a factor, I'd prefer high-speed rail or supersonic Hyperloop stations next to my origin and destination.