I don't really care if they want to know what i'm buying. I don't buy a whole lot of stuff anyway and I don't see why that would be a threat. But it's the fact that they're demanding to know. What for?
But don't they know what you're buying using the old system anyway? The primary purpose of smart cards is the increased security, not tracking (that is already done when you connect to the server).
AFAIK any increase in the recording aspect of it would help them to detect purchase patter deviations more quickly (i.e. if someone else is using your card) and thus allow them to lock your card before too much was lost.
Of course the prime benefits will always be theirs but in this case (rare though it may be) you also benefit.