Not bothering with privacy rules because of on the technical constraints of today's technology is a dangerous game, because when better technology comes along you might find what "everyone does" is already on the wrong side of all the clear lines in the sand.
I mean, 50 years ago it would have been ridiculous to suggest the government could transcribe and search all phone calls - consider the incredible cost of all those typists, filing cabinets and reel-to-reel tapes! If someone had said "because we already have technical constraints, there's no need for ethical or legal constraints" we'd be in a difficult position when the technically impossible became possible.
Sure, but this is no different than smartphones. The parent comment above mine says Glass is a "new form", but it really isn't. It's just an Android device with a worse-than-average camera and a worse-than-average battery life and a worse-than-average capability to covertly record other people.
In the vein that you can buy a pen camera that'll do a much better job for $30, worrying specifically about Glass seems silly.
I mean, 50 years ago it would have been ridiculous to suggest the government could transcribe and search all phone calls - consider the incredible cost of all those typists, filing cabinets and reel-to-reel tapes! If someone had said "because we already have technical constraints, there's no need for ethical or legal constraints" we'd be in a difficult position when the technically impossible became possible.