I don't like it, but yes it should be allowed. As others here have pointed out, we do not have a right to privacy in public, and are photographed constantly by security cameras, cell phones, and police lapel cameras. Why single out Google Glass? Someone mentioned that you can't tell when people are filming you or not with Google Glass, but unless you have omnidirectional vision, someone from some angle might be pointing their cell phone at you. A man could cover up all but the lens of a lapel camera with the lapel on his suit and have the lens peeking out through the boutonniere hole and you would never know it. Likewise, a woman could conceal such a camera behind a large piece of jewellery, with a hole in the middle for the lens to peek out. Even before cameras were as small as they are now, t.v. reporters for 60 Minutes and 20/20 were (somehow) concealing cameras on their persons for hidden camera interviews.
I don't like the idea of being filmed in public. I agree with Richard Wee that if you don't want to be filmed doing something, you probably shouldn't do it in public, but sometimes we do embarrassing things without intending to. I once walked across a crowded pedestrian mall without realizing that my fly was open. It's embarrassing enough to think of all the people who personally witnessed my stupidity, but what if it had been immortalized in a YouTube video? I could have been Open Fly Guy to everyone I met for the next five years, including people interviewing me for jobs. But I don't have a right to privacy in public, and technological advancement will probably continue to make cameras even smaller and more concealable than they are now, making enforcement of a hypothetical anti-camera law nearly impossible. So if I don't want to be on YouTube, I'll have to make sure all my zippers are zipped, that I don't trip and fall in a comical way, and that I never have an emotional outburst in public, be it in anger or over exuberance.