George Costanza
A Friendly Liberal
An identity thief divests an elderly widower of his entire, life savings by tapping into his bank accounts. Afterwards, the theif brags and laughs about his act to others. He is arrested and charged with identity theft and grand theft.
How about charging him with a capital offense on the theory that the elderly widower could easily have died of heart attack caused by the shock of learning that his life savings had been stolen?
We can open up a whole new world of criminal liability here - capital offenses for what might have happened as a consequence of the bad guy's actions.
There are people who are a ticking time bomb.
Society needs protection from them.
I understand your frustration - I think we all share it to some degree. But while "stopping crime before it happens" is something nice to think about, the price we as a society would pay for doing so would FAR outweigh any benefit gained by actually trying to do it.
How do you know someone is a ticking time bomb? And even if you did, how could you be sure that incarcerating them would prevent anything?
Until someone comes up with a legitimate method for stopping crime before it happens, I'm afraid we are stuck with what we have - which is no police action until a crime is actually in progress or has been committed.