> Most humans are altruistic and trusting by default ...

... towards an in-group, yes. Not towards out-groups, as far as I can tell.

Though for some reason this tends not to apply to solo travellers in many, many parts of the world.

Lots of debate, yes, but very little about the basic fact that Hardin's formulation of "the tragedy of the commons" doesn't describe actual historical events in pretty any well documented case.

Wikipedia (https://en.wikipedia.org/wiki/Tragedy_of_the_commons#Example...) does have global examples where tragedy of the commons has applied, like mass extinctions and climate change. These are ongoing but have already caused permanent damage.

Although, there are other large-scale examples where tragedy of the commons has been (practically) avoided: ozone depletion and Polio eradication. Wikipedia (https://en.wikipedia.org/wiki/Tragedy_of_the_commons#Non-gov...) also mentions Elinor Ostrom, but her examples involve "smaller numbers".