The data can be wrong. This could be easily fixed if law enforcement agencies had to actually verify that the data was correct, but in practice this seems to rarely occur.
When people are told by a group that they are a thing, repeatedly, they eventually accept that they are that thing. If the cops keep harassing you for being a gangbanger when you have never been one your whole, you just happen to be associated with a few individuals who are, you eventually just move towards that group. Why not? The powers that be already think you are one and they treat you like one, which causes other people to treat you like one, so why not just be one?
You also need to consider the idea of enforcing crime that hasn't happened yet. That defeats the whole point of law enforcement. It is meant as a reactionary force, not an offensive force. Policing someone who has the potential for crime assumes that they will do it again, which makes it so your essentially treating them as guilty for something they haven't done yet. From my perspective, that seems to defeat the purpose of our legal system.
Anyway, I think I will end my rant here...