If we force police to wear something like Glass all the time, we might as well just have robots doing the job. This would make things to "black and white" for me, and I suspect most people, once it was actually implemented.
I know a lot of people don't trust police officers, but I think we need to leave an avenue open for making common sense judgement calls.
If they are forced to wear Glass all the time, every step they make will be scrutinized and second guessed, I believe this is more than can be fairly ask of anyone doing any job.