> What would you say to someone in 700 AD, for whom the next 1000 years were more likely to be objectively worse in terms of quality of life than the next 1000

Not OP, but I would probably say something like "don't have kids, it's morally irresponsible to bring children into a world where they will have to deal with conditions likely worse and far more barbaric than climate change which causes immense suffering in the future".

Then I'd quickly duck out before they reported me for being a witch.