This is a key point. The problem isn't so much that certain things are done under legitimate circumstances, but that they sometimes happen under dubious or plainly immoral circumstances.
Introducing some friction to the process means there's essentially no significant barrier to doing it but it's still not entirely cost-free; there's some overhead involved making it less likely to happen nilly-willy and increasing the changes that improper action will be caught by some oversight.
By all means lets make it harder for the FBI to get access to Internet traffic, or to telephone logs.
But generally, if the FBI believes it has a car it wants to follow, I'd like them to be able to do that as effectively, cheaply, and safely as possible.
Friction can be a good thing, but I don't think we should add it everywhere just for the sake of it. And remember, one consequence of friction is that it wears things down. The court that says "yes" to hundreds or thousands of GPS tagging requests is more likely to say "yes" to the next search warrant request too; we'd have constructed a system where the "yes" corresponds with the base rate.
I don't see that great a difference between my Internet traffic or phone logs and my daily whereabouts (i.e. my travel traffic and my physical location logs).
Good point about the debasing of saying 'yes' to things; it might end up like the permission system in Windows 7 where you get asked for permission for damn near everything to the point one starts clicking "OK" without thinking.
But having zero friction for trailing anyone, anytime, is also a problem.
I think someone else hit the nail on the head elsewhere when they said that they wouldn't be comfortable with their neighbors doing this. I think that's relevant, because it exposes that normal people do see a privacy interest in having someone follow you around, whatever the law may currently say about the existence or non-existence thereof. Maybe it's not a reasonable expectation, but that doesn't seem right to me, even if our privacy is steadily decreasing.