Hunh, I think that’s the same argument to be used for illegal wiretapping, slapping GPS transmitters on cars, and on an on. "We’re after nasty people, so society’s best interests are served by having us use every tool at our disposal and letting us choose who, when, and why without oversight.” And yes, the answer may be easy for you, but it’s also easy for me. I don’t think the fact that these people may be nasty has any bearing on what should or shouldn’t constitute due process. I also don’t think that discovering their nastiness after the fact justifies the police actions before the fact of their nastiness has been established.
I suspect there are deep, deep philosophical divides at work here. For your reading interest, I present something that happened during the a long-ago spate of successful domestic terrorism events:
https://en.wikipedia.org/wiki/COINTELPRO
Which leads naturally to a group of actually nasty people:
https://en.wikipedia.org/wiki/Weatherman_(organization)
I almost forgot. As a Canadian, I am especially interested in this difficult moral case: