You're right that legal precedent doesn't take rights absolutely. For example, there's the "clear and present danger" test for speech rights. However, weighing

You're right that legal precedent doesn't take rights absolutely. For example, there's the "clear and present danger" test for speech rights. However, weighing against such a determination is what the OP explained: any competent mail anonymizer is going to be a dead end in the investigation, so the chances of a payoff is small. I'd be curious to see the actual warrant, to see what the judge approved them to look for. And on the other side of the coin, I expect that the rights of those using the anonymizer (as opposed to those of the company offering the service) were not weighed, because the FBI never inquired as to who would be affected (at least as far as I know). Those users of the anonymizer are not directly injured, but are collateral damage. However, the same is true of you: you're neither the threat-maker nor the target of the threats, you're just inconvenienced by the actions that the victim was forced to make.