This is not, in practice, what they do. In reality, they tend to use overwhelming force with dubious justification (if any), escalate situations via techniques

This is not, in practice, what they do. In reality, they tend to use overwhelming force with dubious justification (if any), escalate situations via techniques such as kettling of protestors, and arrest/brutalize people expressing their disapproval of the above. There are many instances where police use violence on nonviolent protestors, so how does that protect them from physical harm?