> the carrying capacity of a healthy planet is much less than 8 billion people
Not sure what you are citing for this, but I would assume this is less than 8 billion people based on our current pollution and consumption rates.
This stat is a mind-blowing one also considering the sheer amount of empty space still available on the planet. With good resource management and terraforming you'd think this number would be a lot larger.
Most of the extinctions happened when there were less than 10m people. All the large mammals and birds got wiped out during humans hunting and gathering phase.
Certainly one issue where I'm a bit biased to being part of the problem. Observing things doesn't express a belief necessarily, though it is my opinion.
We could do with fewer people. In 2000 there was ~6.1 billion and the world was just fine.