so world war three
ends fairly
rapidly
the planet is toast
and every last human being suddenly a ghost

benefits are as follows:

carbon footprint = zero
(ghosts don’t need heat, lighting or food, are essentially nude, don’t so much travel places as drift a little when they’re in the mood, so…)

inequality = zero
(ghosts are basically and identically dead, don’t lust after money & power but look vaguely lost instead, everybody draped in a sheet off the bed, so…)

environmental harm = zero
(admittedly starting from a crispy base, but nature slowly reasserts dominion over the place, so…)

risk of infecting other planets = zero
(even if they could build a rocket, they couldn’t ride it, guide it or carry tools in their pocket, and if they landed somewhere they couldn’t lock it, so…)

basically what you’ve got
is a shell-shocked planet that’s smokin’ hot
8 billion ghosts haunting the spot
at least until their guilt’s forgot
which is when, I guess
they’ll all coalesce
into one, long, rapturously heartfelt sigh
and lift like mist to the clearing sky