It's a red flag, not the only red flag. Like, if you use strong encryption, have associated with known drug traffickers, and served time in prison on a felony charge, someone might want to keep an eye on you. It's one of many factors that may or may not be worth considering. The use of strong encryption alone should not be considered bad.
Like in your example, I bet recent association with known drug traffickers is so much of a stronger signal that looking at encryption or felony history is basically worthless. Associating with known criminals is worthy of the label 'red flag'.
My argument also extends to things like the TSA. We all like to complain about having to wait in line for security at the airport. Why can't they do better threat assessment? Well, it needs a holistic approach. Why should I, chrissnell, an officer in the Army Reserve, with no criminal record whatsoever, be subjected anything more than a magnetometer at the airport? If the TSA would look at my profile holistically, they would see that I am not a significant threat and that should mean that I would be able to go on my way without interference.
The elephant in this particular room is that if the government has enough information about you to make these sort of decisions holistically, it also has enough information to effect many, many abuses. History teaches us that trusting an organization like this to "do the right thing" is a fools game.
thats a red flag. you've got specialized training in weapons and tactics. maybe they should "keep an eye on you" ?
This is a domain of probability, there are rigorous ways to deal with that. Bringing up "nothing to hide" isn't a rational response. Whether or not something constitutes a good signal does not depend on rhetorics! Math doesn't care about what some celebrity said at some point.
Locked doors stop boxcutters.
The important thing is - probability theory doesn't depend on rhetorics. Someone speaking the "nothing to hide" argument, or someone else finding arguments against it convincing, doesn't suddenly invalidate Bayes' theorem! Trying to argue from principle is a mistake because reality doesn't listen to principles. The only relevant question is whether encryption/Tor/whatever is or is not currently an evidence for/against being an evildoer, and how strong that evidence is.
Those considerations do include things like loss of utility because of false positives / false negatives, too. So for instance, it may be so that evildoers are more likely to use encryption than general population, but there's so much normal people using encryption that you can't get evidence for being evil out of just noticing that a person uses encryption (the same considerations explain why so much of what TSA is doing is security theater).
Let's say theoretically, that people who wear red shirts are objectively more likely to commit a crime. Policies are made such that people with red shirts are targeted for extra policing. People with red shirts who are not criminals feel discriminated and overly watched, and because of that, generate a resentment against society and (I admit this is a jump), ultimately end up with a higher disposition towards committing crimes. And then it just goes on ad infinitum.
So in some situations, I would argue that society benefits from ignoring these objective probabilities entirely, if there's evidence that taking action based on them could cause downstream negative consequences.
I say in some situations, because the typical case is that if something (e.g. wearing red shirts) is likely to attract attention you don't want, you'll tend to avoid doing that thing (you'll stop wearing red shirts in order for the police to leave you alone). So there's a negative feedback loop. But I can see how this loop can fail in case of things one can't (easily) change - like skin color, cultural background, religion, etc. This leads me to believe that just looking for probability-based signals may be a good thing in case of guns and encryption, but a bad thing in case of race and religion.
I think we need to be careful not to argue law from probability theory. While as you've pointed out many things will not actually be predictive of "being a terrorist" (whatever that means) there will be things that _are_ predictive. But we mustn't let the predictive nature of the information be in and of itself justification for obtaining it. There needs to be respect for constitutional limits on the reach of government, regardless of what the math says.
But unless there are strong reasons to do otherwise - for example, what 'wakkaflokka pointed out in a parallel comment may potentially be such a reason - I do think we should derive rigorous conclusions from the data we already have based on math, and not on rhetoric.
It's super clear that we're on the cusp of a total informational transformation in the West in terms of how life is lived, and a consequence is that there are deluges of personal data.... and a lawful, diligent and trustworthy law enforcement or spy officer will want to use that to do their jobs better. Unlike many in the tech world, I don't buy into either left or right anarchism: I think the office of the State is a valid one.
So we have to start looking to the future and how to properly safeguard rights in the Information Age.
what good will that do if the suspect is using encryption. thats the whole point!
Is encryption door lock(which in the real world are trivial to bypass in case of valid warrant) or Bond villain's lair?
Encryption is red flag because so few people are using it.