[darawk]

That's true, interesting and important. But I don't think it addresses the intent of my point, which was that there are plenty of odious organizations that are abiding by the letter of the law in public, but may well have members or private discussions that are likely to tend into serious criminality or terrorism. The KKK is one example, as are right-wing militias, etc. I think it's important that the government be able to conduct some basic level of surveillance on their activities, even without any direct evidence of a crime, or intent to commit a crime.