Most of these scumbags need it. A day in court with an asbo or small fine is not going to get the message through their thick skulls the way a little bit of smackdown will.
"Now see here you ne'r do-well rapscallions! You will refrain from hitting me with broken bottles and bricks until my fellow police officers arrive with the neccessary equipment to detain you! It shant be more than a few minutes or so." And you know how American crooks would deal with "stab-proof" vests? Get longer knives!