Is a "Global passive adversary" only theoretical or is it an actual thing? : OpSec | Torhoo darknet markets

Using a safety belt is basically losing time because if a tank roll over your car you are anyway dead so lets all throw away all our safety belts ... good idea or not?

In the real world, no, because governments would need to share info with each other, and that can't happen because of political tension.

NSA has checkpoints at various locations in US internet backbone. They can watch the encrypted Tor traffic there. But they can't watch traffic in European Union, and they can't watch traffic in Russia. EU and Russia are likely watching their own countries, but not sharing data with each other. Do you really think Russia would send their surveillance data to US? If they all worked together, then yes, they may be be able to denonymize Tor traffic.

A more likely scenario is they attack Tor's directory authority servers.

In both cases, you lose anonymity but not security if you only visit hidden services and HTTPS websites. They still can't see what you're doing on each website. And to the website or hidden service, you're still anonymous.

The closest thing to a global passive adversary would be something like the 5 or 14 eyes, which is a data sharing partnership between all of the major western spying agencies in the world. Pretty much all of the autonomous systems which comprise the tor network run under their combined jurisdiction, so they would fit the definition of a global passive adversary easily.
A "global" adversary could also be one which just sets up a large number of tor nodes until they had control over a significant portion of the network.

But I think that even considering known traffic correlation attacks in existence, the number of false positives is high, even attacks which claim "99.9% accuracy" due to Bayesian Detection Rate Derivation. The difficulty only becomes exponentially higher the more people use the network. That's why it's important to use tor all the time and to encourage everyone you can to use it as well. Check out this write up for more info on why traffic correlation becomes much harder as the number of tor users grows: https://archives.seul[dot]org/or/dev/Sep-2008/msg00016.html