I agree about the already-known argument. The Charlie Hebdo murderers, the Boston marathon murderer, Lee Rigby's murderer, they've all been known to the police

I agree about the already-known argument. The Charlie Hebdo murderers, the Boston marathon murderer, Lee Rigby's murderer, they've all been known to the police and/or intelligence services. In which case, a pertinent question to ask is if the aim is to stop such attacks, is it appropriate to spend this much time and effort building a bigger haystack on top of the needles they already have?