The problem is not that it doesn't make things better. The problem is where, how, and when it will be abused. (It's 100% certain that there will be no if, because we all know that the government already gathers as many reins of power to itself as it can grasp.)
This is the concept that most people don't recognize. Most people say\think that its all good to protect the children or catch the terrorists. But what happens if you are in that database and some government entity unlawfully decides that your class of people, whatever it may be, needs to be disenfranchised, persecuted, or even killed off?
People will almost always say that those things can never happen here in the US. It happens in other places in the world but never here. The reason it doesn't happen here, for the most part, is because we have been, and must be, ever vigilant for these kinds of abuses and crush them when they start down that proverbial slippery slope.
Don't open the door to the possibility of it happening and it never will. By allowing this type of scenario to occur we are definitely opening the door.