I agree. The main problem is that it’s impossible to reliably project out even decades let alone centuries or millennia. So longtermism gives you this blank slate to tell any “just so story” you want.

Speculating is fine but you can’t use pure speculation to justify things in the real world. That’s the problem.

Truth is that we have no idea about anything much past our own slice of time. In 2000 years we may be extinct, reverted to hunter gatherers, settled across the solar system like in The Expanse, or extinct or kept in zoos by superintelligent posthuman AIs that have expanded out into the cosmos. Or none of the above. Who knows.