First of all, the Gentle Giant had attacked the officer once, and was approaching the officer again. Do you think he was just volunteering to sit down in the police car? It finally took a shot to the forehead to stop him. If the officer did not shoot, he might likely have ended up dead, and Brown would be traipsing around North County with a dead officer's service weapon.
Secondly, if you think the police are so bad, take a look at what happened when there was no police.