If you have the choice to buy or not to buy at the shop, that's fine, it is your decision. But let's imagine that in the not so far future, all shops in your neighborhood are like this. No way to go shopping whithout given exact trace of you, your location, the stuff you buy, the time you buy, the amount of food etc.
We all know that too much data is not good for us (yes, I am looking at you, my government).
While I like the idea of not standing in a line and wait, I really wish that these shops offer a prepaid anonymous card for those who don't want to be totally tracked.