> Seriously, you could apply this to any hobby if you want to use an endless list of externalities.

I don't think you could. Fuel is one of the most mispriced things in the world; airlines may not be paying pennies a gallon like certain countries wastefully subsidize fuel in their countries, but it's pretty blatant that fuel subsidies of every kind are enormous, and they've been particularly singled out by economists like the IMF as wasteful.

> It's not like the plane would be sitting on the Tarmac if he didn't board it. It's flying anyway.

On the margin of plane flights, there would be fewer plane flights if he didn't have this 'hobby', and much more directly, every flight he boards wastes a lot more fuel simply carrying his weight.