His hypothetical literally described the standard for getting a warrant.
Probable cause is based on evidence.
> His hypothetical is actually how warrants are supposed to work.
No, its not.
> Law enforcement have probable cause to suspect someone of being guilty. If they can make a strong argument about why the person is probably guilty, they then get a warrant to search for evidence in homes, phone calls, emails, whatever.
And that "strong argument" is based on factual evidence that was either received through mechanism other than search and seizure, was the product of prior search and seizure in conditions that do not require a warrant, or was the product of prior warrant-based searches and seizures.
If there was no evidence left other than what was sought in the warrant, there would be no basis for probable cause to support the warrant.
> Probable cause is based on evidence.
From wikipedia, "Probable cause" is a stronger standard of evidence than a reasonable suspicion, but weaker than what is required to secure a criminal conviction.
In other word, you can get a warrant when you don't have enough evidence to secure a conviction, which in turn may lead to gather sufficient proof of guilt (or exonerate the suspect, I suppose).
Again, if there is no evidence left by the "hitman" except the calls for which the warrant is sought, as specified in the hypothetical, than there can't be probable cause to support the warrant. There can't even be reasonable suspicion. In fact, without some kind of evidence, the only thing that could support the desire to seek the wiretap is arbitrary prejudice.
Nobody is arguing against that. What people are complaining about is, among other things, the bulk collection and retention of records; the gathering of records upto 3 degrees of separation from a suspect; etc.
And, even if the FBI could know that a hitman left a series of incriminating phone calls without already having evidence which could be admitted against the defendant of the content of those phone calls, a wiretap based on a warrant issued after the fact wouldn't recover those contents.
Further, I don't think anyone in the thread has argued that wiretaps aren't useful in criminal prosecution, the issue which started this was a poster expressing that it would be wonderful if wiretaps were categorically outlawed, which does not require believing that they aren't useful in certain circumstances. It could, for instance, proceed from the belief that the capacity is so likely to be abused covertly in circumstances where it is inappropriate if its existence is tolerated at all, that the usefulness it has in the circumstances to which it is appropriate is outweighed.
Now if someone tells the police that they've been getting incriminating phone calls, well then that seems like more reasonable probable cause, and doesn't strike me as morally dubious.