Not only is it a potential violation of privacy, it can also serve to put Americans at risk overseas.
The new RFID passports send a signal, but what happens when bad guys get a card reading device, or perhaps plant an explosive device that is set to detonate ONLY in the presence of certain RFID signals.
100 tourists could walk by a garbage can and nothing happens, ...but the American with the American passport walks by, ...and it triggers the detonation of the explosive devise.
Soon, it will get to the point that no American could ever again pass themselves off as Canadian when overseas, ...no matter how polite and courteous they may be, ...they'll stand out like a sore thumb, ...or if their RFID passports trigger detonators, ...they'll stand out like servered thumbs and other various body parts. Most garbage cans are waist high. Can you imagine what could happen to you if a devise goes off at waist height?