this is a particular kind of fallacious pro-technology argument that deserves some attention: "it has a good use, so it should be allowed." this is a fallacy because the good use doesn't discount or prevent the bad use. they are, generally, entirely separate issues.
Further, in this case, there are specific technologies available and in development to do the driving-specific tasks you name.There has already been controversy about computer technologies in automobiles not directly related to driving. I believe the state of law and industry practice right now is that HUD interfaces that give driving information, like dashboard tools directly related to driving, are acceptable, but that there is great concern over displays (even ones for controlling the stereo, heat of the car, etc.) that aren't directly related to the road in front of the driver. This is why GPS systems get locked out, even though they are directly related to driving--even the little bits of interaction drivers do with them can be distracting. People wildly overestimate their ability to focus on such tools, even when they are related to the drive. (I include myself.)
the issue with Google Glass has nothing to do with this: it is the availability of tools *not* related to driving. slashdot readers know that there is no way to put a "lock" on Glass that creative users won't get around.
if and when someone develops a HMD that is solely devoted to driving, I suspect that would have to be legislated separately, although it's hard to see why that would be more useful and/or not integrated into the manufacturer's HUD.
Of course, Google's Driverless Cars will soon make much of this moot anyway. Sort of.