Are there examples of very lightly regulated housing markets in developed countries? Does that really lead to bad things like people say? I know it can cause sl

Are there examples of very lightly regulated housing markets in developed countries? Does that really lead to bad things like people say? I know it can cause slums in poor countries. But would California or Vancouver somehow fail if they allowed unlimited high density construction and development in what's currently undeveloped land? Are there examples of that happening before?