I'm confused why it's a privacy nightmare. They could just as easily sit someone there and count how many people are in a store and write it down. Your face is an identifier. I don't get why people think that anything technological anymore is instantly privacy nightmare. For an often technological website there is so much technophobia.
The difference is one of precision, scale, and duration.
Also in terms of cost, there's a difference between tracking which imposes a marginal human cost of production versus tracking which can be fully automated by machine, even if there is still a per-machine cost.
A relevant example is the Supreme Court ruling on needing a warrant for using a GPS tracker on a car versus just tailing them.
The difference is that this is equivalent to having that person follow you to the next business you shop at... and the one after that... and the one after that...
