During COVID, airlines flew empty planes back and forth at a loss just to keep the right to their established routes and air ports.

What nonsense. I certainly feel like a medieval peasant sitting in a high speed train crossing a large country while I read a book for a few hours, costing three hours of work at the median salary if you book your ticket far enough ahead. (They also allegedly run on wind energy, but of course that's creative accounting and another industry is simply attributed the corresponding amount of coal/gas electricity.) Traveling is accessible, fast, and comfortable. The main expense is the hotel(s)

It's about 60 mpg per passenger to fly domestically and 90 mpg per passenger to fly internationally.

If you have a family of 4, you can think of it as the equivalent of a 15 mpg vehicle for domestic flight and 22 mpg vehicle for international flight. So somewhere in the range of a full-size pickup truck.

But -- when you fly, you go very far. If you go on vacation to Hawaii from San Francisco once a year with your family, that's the equivalent of driving a Ford F-150 for 5000 miles. If you visit India or China that's 15,000 Ford F-150 miles! In a single trip, more than what most people drive in an entire year!

So you can make a big difference just preferring local vacations instead of remote ones.

It's code for "don't travel, especially long distance"... because most people would simply not be willing to make many trips if the trips took as long as the non-flight option would require.