How good would the abolition of zoning in New York City be?

Yes, I am opposed to many forms of zoning.  Without zoning our cities would be denser, more eco-friendly, cheaper to live in, more able to produce economies of agglomeration, and more immigrants would benefit from American prosperity.  Matt Yglesias periodically has good posts on this topic. 

More specifically, Manhattan would look more like Sao Paulo, with a true forest of skyscrapers instead of the current puny and indeed embarrassing line-up.  Many of these towers would be residential, as they are in Sao Paulo.  Many problems of cities, including congestion, would of course become worse.  Overall I see the gain as real but a small one, at least relative to gdp.

A key question is what zoning means.  Let’s say you wanted to set up a shack on the sidewalk and live in it; should that be allowed?  How about a modest apartment building but without a water connection?  Should Manhattan really become like Sao Paulo?  Only in extreme cases would I wish to waive such infrastructure requirements for the housing stock.  And if you agree with me on that one, then you don’t want to get rid of most zoning either.