That's a fair point, but I'm not sure where I'd draw the line. The worst consequences you cited -- identity theft, fraud, etc. -- are already illegal.

The best I've come up with so far is that when it comes to prior restraint, you have to consider (a) whether there is an effective remedy to undo any damage after the fact, and (b) whether there is any legitimate reason to do whatever you're proposing to restrain, and if so, what the adverse consequences might be. Then it's a balance, and personally I think it's safest to bias against any form of prior restraint if it's not a clear case.

In this case, once a severe privacy invasion has taken place, often the consequences are permanent. Sure, your kid might have another birthday and still enjoy the new toy, but you'll probably never get another chance to propose in the way you've spent the last six months planning and see the look on your wife-to-be's face before she says yes. I would have no problem with severely punishing someone who thought it was OK to deliberately spoil that kind of special, once-in-a-lifetime moment. On a more objectively measurable level, you'll never get back the three months of your life that you'll probably spend chasing banks and fixing your credit records if someone steals your identity.

I'll note in passing that none of this is the really bad stuff, which is less likely from my example of just being followed around for an afternoon but all too possible in a world of ever-increasing surveillance and data mining. The really bad stuff is probably when your career and/or private life get destroyed by an untrue allegation that taints your reputation irreparably. No amount of retractions and apologies printed later is going to remove the cloud of having once been accused of privately being a little too friendly with children, or abusing your spouse, or botching a medical procedure that left a patient permanently disabled, or stealing your client's private records and selling them to the competition.

That's the "can the damage be undone" side of things, so what about the damage from restricting the other action?

When it comes to someone following someone else around and systematically recording their behaviour, I find it hard to see any legitimate reason for doing it at all, other than genuine security/law enforcement considerations, in which case the usual caveats about due process and independent oversight must apply.

Just to be clear, I'm not talking about merely being in the same places as someone else here. That could happen coincidentally, and clearly there is a severe negative consequence to trying to prevent one person moving freely just because another happened to go the same way, as well as it being completely unrealistic. I'm more concerned about the kind of active surveillance I mentioned, such as someone deliberately following you and recording their observations. Perhaps more realistically, I don't see any real difference in privacy terms between that scenario and the use of an automated surveillance system that allows a similar picture to be built later by data mining, whether that is from CCTV cameras and facial analysis around town, or a cell provider recording the location of your phone, or your ISP logging all your Internet activity, or Google/Facebook tracking your web browsing history via beacons, bugs and other dubious practices. If anything, the latter type of surveillance is worse, because at least you can see the guy following you around and peering over your shoulder or through your home window.

(In case anyone's wondering, the proposal-related example came to mind because a popular wedding venue near where I live recently burned down. Obviously if that was a deliberate act of arson then it was criminal anyway, and the loss of the buildings and revenue to the operators was severe, but the really heartbreaking thing reading those stories was the idea that what should have been the happiest day of some couples' lives was going to be ruined because there wouldn't be time to make other arrangements. When it comes to issues like privacy, it is often the personal, emotional consequences rather than some measurable financial or practical cost that are the most damaging, and I think it is regrettable that many legal systems seem to assign little if any weight to such harm.)