Do you expect 40000 UQAM students to all live in the Quartier Latin?
Why? They say you will meet 10,000 people in your lifetime. What is to be gained by having the 30,000+ other people there?
What if you have a couple where one works at the Botanical Garden and the other at the National Library that are in different parts of the city?
What if they got jobs locally? You can't have a local economy without local workers.
Dense, livable cities cannot exist without public transit.
There exists communities in this world with over 150,000 inhabitants in a square kilometre. What is the 150,001st person providing you that the 150,000 other people can't?
By dense, are you imagining having a few acres of land to call your own? That's fine, but that's the rural life, not the city life. If you want to live rurally, why not live rurally?