Suburbia isn't safer, isn't cleaner, isn't cheaper.
Indeed, violent crime per capita tends to be higher in less dense areas.
Also, the suburban lifestyle is dependent on the automobile, so walking simply isn't an option - even for everyday tasks like picking up a gallon of milk. More driving means more fast-moving cars (speed limits tend to be higher in the suburbs) and more opportunities for bad accidents. Moreover, the unintended impact on health is obvious: less walking leads to more heart disease and other illnesses caused by sedentary lifestyles.
Perhaps most shocking, the suburban lifestyle is quite costly. While it's true that housing costs are lower, this is totally offset by the higher cost to service (e.g. utilities, taxes) larger suburban houses and the cost of transportation. Most suburban households are two-car domiciles. The average annual total cost of car ownership is about $9000. In contrast, an urban household can manage perfectly well without a car. This $18000 annual difference equates to a lot of mortgage! Moreover, many suburbanites still must take some form of public transportation to get to work so their transportation costs are effectively doubled.
I'm clearly generalizing, but the tradeoffs and total costs must be considered when deciding where to live, work and play.
Retail is dying. Strip malls are dying. The climate is dying. The average urban dweller in the US has about 1/3 the carbon footprint of the suburban dweller. It's time to re-think where we live and how we live.
The following Ted Talks examines the case for taking back suburbia.