Should the police be in attendance at demonstrations? Absolutely yes. Should they collect photographs, names, addresses, numberplates? No absolutely not.

Let's not forget how easy it is for data to get corrupted. About 12 years after I had married, US Social Security Administration and the IRS, linked databases suddenly dropped my married name from my record and reverted back to my maiden name.   Every year after that happened, I had to resend my birth and marriage certificates to get my married name reinstated. Why? Something to do with how the program kicked over from IRS back to the SSA, would strip out, my married name. They could never figure out why. They weren't fussed, I just had to get it changed every year before April 15 when taxes were due. What a pain in the ass.

So what is to prevent a table of peaceful protesters and a table of terrorsists, getting all jumbled up in the "Extremist database?" One wrong entry and John Q Public who refused to cross a picket line one day, whose name and picture is now in the database finds he is marked for life because an errant keystroke checked the "dangerous" field on his record. How the hell do you fix that?