while i generally find your articles thoughtful i think this one falls into the north american fallacy of equating density of population accommodated with height of towers.  however, if you look at some of the most livable cities these are predominantly low rise; paris, barcelona and even new york once you get to the areas around central park.

the city of paris has an area of 41 sq mi and a population of 2.2 millions compared to the city of toronto with 240 sq mi and 2.7 million.

these numbers are achieved because most streets a lined with five or six story buildings with shops on the ground floors and accommodation above. this is the classic paris streetscape.

by comparison there are long stretches of king, queen, dundas and bloor streets and eglinton and lawrence avenues  that have buildings of only two or three stories. if slightly higher buildings replaced the present structures density would rise and livability maintained.  there are two examples on bloor just west of jane.