Speed cameras only operate on public roads. The camera in the store is operated by the store owner. In both cases one of the parties involved in the transaction (driving, purchasing) is involved in enforcement. It is clear in both cases that these measures protect everyone and they have clear limits also.
Better examples would be police searching your home all the time, whenever they want (This maps to device encryption).
Or store owners surveilling competing stores / forcing people to wear cameras 24/7 "to improve the customer experience" (This maps to what Facebook / Google try to do, or what internet wire tapping does).