> Because the police have an obligation to investigate. By mixing personal usage with the Tor traffic, you've muddied the source of the offending traffic, and given them something they can investigate, even if just to remove a suspect.

The whole issue is that it doesn't give them someone they can investigate. There is no more reason to suspect the exit node operator any more than anyone else. Investigating people effectively at random is nothing more than a fishing expedition and a waste of police resources.

> Is the mere presence of a Tor exit node enough to deter the investigation? If so, everyone even considering doing anything illegal should run one.

I'm not sure why this is supposed to be such an unreasonable result. It's the same result you get as a Tor client rather than an exit node and the same result you get when using public wifi at a coffee house or anywhere else. There are a hundred ways to get an IP address that isn't tied to you, why is this one special?

> First by police discretion (by whether they try to obtain a warrant), and then by the judge involved.

That isn't how, that's who. By what criteria are the police or the courts supposed to make the decision?

> For example, investigation of an active terror threat. The reward is so high for active seizure of someone involved, and the possible risk so great for not breaking up the network, that a raid on the exit node operator might be worth it even if the likelihood of them being complicit is very small.

I'm not convinced that the severity of a crime should change the standard for probable cause, but even accepting that premise, the problem is still that the existence of a Tor exit node takes the probability that the traffic originated at any particular place to 1/(population size). Any justification to raid the location of the exit node would apply equally to any other place that could have used the exit node. You're trying to justify the search with an argument that could equally be used to justify a general warrant.

> There are more people around, it's harder to hide a crime when other people may have witnessed a part of it, even if they didn't know it at the time.

This doesn't really apply to almost anything that could be done via the internet. You can see your coworkers carting off toxic waste to be dumped in the river or conducting in person meetings with the victim of a scam. If you see them sitting in their office typing things into a computer, what is that supposed to provide evidence of?

> The leaders of the business likely would want to help the police and not the criminal (for many reasons, both selfish and altruistic).

Which obviously doesn't apply when the leaders could be the ones engaged in the criminal activity, and how are you supposed to know? Even regardless, what are the leaders supposed to do? One of their employees or customers signed into the company guest network with a personal laptop and did some illegal thing. The company has no way to know who it was and no authority to search all their employees' and customers' personal devices, and the device may not even be on company property anymore.

The inability to determine the source of network traffic is clearly a problem for investigators, but it isn't a problem you can reasonably solve by issuing warrants against scads of innocent people. It's a problem you solve by tying the crime to the perpetrator in some way that doesn't apply equally to innocent people.

> Providing for ambiguity in the source of criminal behavior will lead to ambiguity in the application of resources to investigate that behavior.

I don't understand why you think this mixing together of traffic is supposed to change anything. If you pay for both cable internet and DSL and use one for your own activities and the other to operate an exit node then there is a clean separation between your traffic and the traffic of the exit node, but how is that supposed to make any difference? You still control the IP address of the exit node and therefore could still have used it for criminal activity, as could anyone else.