No, I think you're taking it too far. We only need to conclude that the minimal benefits from the proposal (i.e., few attackes would actually be averted) are va

No, I think you're taking it too far. We only need to conclude that the minimal benefits from the proposal (i.e., few attackes would actually be averted) are vastly outweighed by the extreme cost to our civil liberties. There do exist more reasonable compromises. For example, we as a society have already said that you can search someone's property if you get a court order. That's a smaller cost, because the authorities are forced to go through a supervised process before anyone's privacy is in jeopardy, and it's still sufficient to find the evidence in a huge proportion of cases. But the proposal on the table is extreme. It affects everyone's privacy, before there's even a notion that a crime has been considered.