Personally I'd be okay with the population being 10% its current value (though I don't see any non-apocalyptic way of that coming to be). In any case, I think we should decrease our population to whatever extent possible.
But I guess that's just my opinion.
edit: I'm not really sure why you're being down-voted. You're just expressing your opinion here.
But I guess that's just my opinion.
edit: I'm not really sure why you're being down-voted. You're just expressing your opinion here.