When someone's using the roads to travel to kill people, knowing who travelled to whom to trace them to the source is suddenly very reasonable.
No wait, that's insane, we should never expect that it is reasonable to conduct mass surveillance on all the roads in the country to find out where people go all the time.
Why do people think this kind of stuff is reasonable and positive for society?
Utility and traffic light poles have cameras and license plate scanners that can capture up to 5000 plates/sec, even in smaller suburban areas, at an increasingly alarming rate.
EZ Pass and similar are scanned in lots of places that aren't toll plazas — at least that is possibly agreed to via a terms of use.
I was on a jury where the police were able to track down a hit and run driver who killed a teenager within about 45 minutes due to red light cameras.
Torture is a good example.
Mike Baker talks about why it was pointless for the CIA to torture someone and why when they train people how to handle being capture, they tell them to tell the truth with a little information redacted.
However, cellphones in particular do require the cellphone network to track at least which cell they're in in order to work, so in practice controlling a cellphone network gives you a pretty good idea of where all the subscribers are.
This is a big problem, and we need to figure out how to stop it if we are to enjoy the sort of freedom from government surveillance that people everywhere enjoyed since the Paleolithic until about 01998. The 20th-century results of giving too much power to governments are not promising.
"Reasonable" changes over time, with available technology, and with the tolerance of the public. People don't much care for "We could've stopped that murder / caught that murderer, but we didn't use the resources available."
If there's a murder on a street corner, do we expect the cops to not pull camera records from every nearby store with an outward-facing camera?
Not to mention, a trove of communication like this is a major risk to every citizen: it can leak, it can stolen, it can be used by corrupt agents to blackmail or otherwise coerce most people, especially in the age of sexting, dick pics, etc.
The Penn family was trying to buy their way out of having their American land-holdings taxed by offering to pay mercenaries to protect the Colony (in a single lump sum). Franklin was arguing the Colony should assert its sovereign right to tax the family.
The "essential liberty" in question was the liberty of a government to levy tax as it saw fit to provide for a common defence.
When someone's using the mail to send anthrax to people, knowing who communicated with whom to trace it to the source is suddenly very reasonable.
Dying from anthrax is a lot less convenient than having record of every letter a person sent or received dry-rotting in a data warehouse somewhere.