This has little to do with the existence of zoning laws themselves, but the specific zones that they define. Japan has zones, so does Spain. But there's just nothing anywhere near as Restrictive as most US cities' R1 zone. Many places have R2s and R3s that are still more restrictive than the least dense thing than a Spanish city has.
Remove zones alone, and HOAs will get areas into legally binding covenants that are also just as tough as their current zoning regulation.
To solve the US density issue, localities have to be severely restricted in what they can block, but we also have to look at the bigger picture: What is making people want to restrict their neighborhood to extremely low density suburbs? The answers are very uncomfortable.
Remove zones alone, and HOAs will get areas into legally binding covenants that are also just as tough as their current zoning regulation.
To solve the US density issue, localities have to be severely restricted in what they can block, but we also have to look at the bigger picture: What is making people want to restrict their neighborhood to extremely low density suburbs? The answers are very uncomfortable.