100 dollars for a plastic printed ball seems... excessive.

Edit: Turns out it's not. Holy Baloney those things are expensive.

Perhaps in this context the "temperature" is the equilibrium point between incoming radiation and radiated energy for some idealised spherical cow.

There's very little convection in a vacuum so radiative cooling and insolation are the main variables in calculating temperature.

Earth is perfectly sustainable.

Humanity, not so much.

Splendid. The children of these freely associating economic actors... do they get the option to fly back to earth free of charge?

Ah yes, free market slavery.

"It's my way or the airlock".

Developing the toys to colonise mars has benefits for earth based industry and commerce.

Alternatively, you can get earth based money to pay for the development of your martian colonisation equipment.

The chances of earth being hit with an extinction level event are non-zero. The chances of mars being hit with an extincion level event (once a colony is established) is non-zero and higher than those of earth.

People migrate to new and exciting places to get away from what they consider the unpleasant situation they're in. Mars has no laws, no taxes and provides the perfect canvas for authoritarian "anarcho capitalists" or libertarians to set up their utopian future. Then they get eaten by bears.

Alternatively, humans have mismanaged the life support system of this spaceship for centuries so it's time to man the lifeboats and try to find a simpler spaceship rather than wait until this one fails.