Thanks for posting. I find Megan McArtle to be a very thoughtful and prolific writer.
As others have noted, Costco is a membership club that carries higher end products and limited inventory. They are located close to, and cater to, higher income areas. Their customers buy only certain items there.
One additional benefit to Costco is that being a warehouse club, they have a much smaller shrinkage due to theft, because of the membership required to enter the store, and the limited number of small higher priced goods that are typically targeted by shoplifters such as cosmetics.
The whole argument is a fraud by the usual leftists looking desperately to justify their arguments.
Having to pay to get in, uh, adjusts the demographics a little, from an economic standpoint. Po’ folks who want a giant TV can pay for their membership multiple times in a year out of what they save (this 40” 1080p 4 HDMI Philips was a shade over $300 in 2012), then just quit. :’) Familes will save on food and (depending on how stupidly they eat and/or shop) eat better.