Earlier quoted context omitted.
Too much density decreases the quality of life. Overcrowdedness, very long waiting times at every establishment or government office, increased ease of pickpockets etc. to "disappear into the crowd", higher prices. You already see all this in many existing cities; you want that, but worse? I'll take malls connected by highways over that any day. Malls are nice and cars are a better experience than transit/walking in…
More density allows more establishments and offices to exist, and of more different kinds. In a city with 10x the people, you can have 10x more shops, restaurants, etc, and you’ll as result also get 10x more variation.
This point is made well in this article:
http://newworldeconomics.com/how-to-make-a-pile-of-dough-wit...
>Our basic goal, in all this, is to deliver roughly triple the density as this “New Urbanist” model, while still preserving what looks very much like a “traditional Small Town America single family house,” including a nice backyard and lush, tree-lined streets. This is what gets us from 8,000 people per square mile, for a typical Los Angeles suburb (with 5000sf plots), to maybe 10,000 for the New Urbanist example and more like 25,000-30,000 for our example. We have already seen how our basic house plot shrinks from 4000sf to 2000sf, which doubles the density right there. We even have some smaller house plots of 1,250sf and 625sf. Then, we have a huge amount of land now being consumed by vastly excessive roadways and associated Green Space, that we can replace with Really Narrow Streets, thus freeing up more land for houses. For example, if the house plot/total land area ratio rises from 50% to 75%, that is a 50% increase in density right there. The combination of half the lot size plus a 50% increase in density due to reduction in land used for streets/Green Space/parking lots gives us our triple density bogey. Triple the density means that every store or restaurant now has 30,000 people who are within an easy walk of 15 minutes or so, which means that they can have a viable business without a parking lot. It means that every school now has three times as many students that are within an easy walk. No more chauffering your kids to school. No more school buses. At 30,000 people per square mile, and if 15% of the people are school age (6-17), that means 4500 kids are within walking distance of the school. It means that the four-year high school would have about 1500 students, all within a half-mile walk of the school. It means that, if a train station is introduced later, three times as many people will be able to walk there as well. In short, everything becomes a lot more “walkable.” By making it walkable, we thus eliminate the need for cars unless travelling outside the immediate neighborhood, which eliminates auto traffic and also makes the neighborhood much more peaceful, quiet, and suitable for kids, families, and seniors.