Direct-mail advertising usually consists of advertisements for products to be purchased from the home, so the perception that it is bad for the environment is misguided.
Conclusion
The perception that direct-mail advertising is bad for the environment is misguided. (i.e. direct-mail advertising is not bad for the environment)
Evidence
Because of direct-mail advertising, millions of people buy products by phone or online. These products would otherwise require use of a car to go buy, and the car would add pollutants to the air.
Evaluate
The author's argument is that direct-mail creates a Net Gain for the environment (or at worst it's neutral).
She thinks that there is an environmental "savings" happening because people are buying products that are then shipped to their house, rather than driving to the store to buy them.
We have to analyze all the environmental tradeoffs between the world with direct-mail advertising and the one without.
With direct-mail, they aren't driving to the store to pick up the toaster they ordered, but isn't Target driving the toaster to their house? Are we sure that the exhaust saved by the customer not driving to pick up the toaster isn't offset by the exhaust used by the Target delivery driver bringing it to their house?
Maybe personal vehicles are more likely to be electric / low-emission, whereas delivery trucks are more likely to be gas-guzzling / high-emission.
What if it's less environmentally efficient for me to have Target and Pier 1 and Bed, Bath, & Beyond all deliver me stuff than for me to get in my car and drive to the shopping center that has all of them in one place.
We also have to consider the environmental harm of all the paper that goes into sending out the direct-mail ads. What resources are used to make those ads? What damage is potentially done by all the direct-mail trash?
Goal
The argument would be weakened if we could say
So we can strengthen this argument by ruling out any potential environmental cost.
We can also strengthen by learning any information that makes direct-mail sound more environmentally friendly, or that makes the direct-mail World seem more environmentally friendly than the world without direct-mail.