"Too few ideas." I don't think this is true. If anything, we might be getting too many people and not enough ideas, as a lot of people are making niche products just so they can invent something.

I don't have a good argument to defend this, because there's no way I could predict how civilization, technology, etc. could advance if we had 8 million people instead of 8 billion. But intuitively I just don't see it being much different.