The only deterrent of crime is the fear of getting caught, no matter what.

If you let those breaking the law dictate the rules for engagement so controlling the rules for capture then there will never be an effective police procedure. Tail wagging the dog.
Imagine the same rules applying to guns..
Someone with a gun is shooting road signs, shop windows, street lamps etc in a built up area of auckland cops turn up ask him politely to stop, he says piss off I know you cant do anything in case I start shooting into houses, they recognise him from many, many other "events" so walk off with the intention of catching up with him sometime later.
We don't want to cause a problem now do we, might get some people complaining about police on the website kiwi gunner.