We don’t know if Facebook has some kind of Paedophile-o-Meter. But, given the extensive user analysis it already does, it probably wouldn’t be very hard to build one –and not just for scoring paedophiles. What about Drug-o-Meter? Or – Joseph McCarthy would love this – Communist-o-Meter? Given enough data and the right algorithms, all of us are bound to look suspicious. What happens, then, when Facebook turns us – before we have committed any crimes – over to the police? Will we, like characters in a Kafka novel, struggle to understand what our crime really is and spend the rest of our lives clearing our names? Will Facebook perhaps also offer us a way to pay a fee to have our reputations restored? What if its algorithms are wrong?The promise of predictive policing might be real, but so are its dangers. The solutionist impulse needs to be restrained. Police need to subject their algorithms to external scrutiny and address their biases. Social networking sites need to establish clear standards for how much predictive self-policing they’ll actually do and how far they will go in profiling their users and sharing this data with police. While Facebook might be more effective than police in predicting crime, it cannot be allowed to take on these policing functions without also adhering to the same rules and regulations that spell out what police can and cannot do in a democracy. We cannot circumvent legal procedures and subvert democratic norms in the name of efficiency alone.