I'm sure they'd love to know every appliance and electrical device we have and and when we use it as well. To know exactly when we leave the house, which rooms we use and when, what a great tool for the police and the good guys.
OK, except SmartMeters can't do these things, so why bring all this up?
Limited to only the pure amount of electricity used and generally when is completely reasonable, but it is a slippery slope to them monitoring what we are using.
How would they determine what we are using? And really, why would they care? Do terrorists run their dishwashers at odd hours?
Given all the real privacy concerns out there, that you outline, this has to be the crappiest way to gather intelligence about someone. Given that all your mail goes through the postal service, your phone calls through a single land line carrier, and your internet through a government-controlled internet backbone, and your TV viewing habits through a digitized box that tells the cable company what you are watching and when, how is knowing your hourly electricity use a big deal?