Police power is legislated by the government.  The limits to which law enforcement agencies can act is clearly defined by the legislation and, where there appears to be a grey area or it appears that law enforcement agencies have overstepped their bounds, the legislation and grounds for using their powers (granted by the legislation) is tested in court and decided on by the judge/magistrate.

 The determining factor for the level of authority a piece of legislation grants a law enforcement officer is therefore up to the government, and so could be affected by the weight of public opinion.  If enough people believe that law enforcement is too draconian, then they could lobby government to change the legislation and limit the power that law enforcement agencies have.

  If people seek to stop law enforcement from doing something they have the legal right to do, then clearly the people need to stop and think about what they are doing.  Civil disobedience is fine and sometimes encouraged to show the peoples displeasure, but it can be done passively or in a threatening and violent way.

 Attacking law enforcement officers because you see the system as flawed, is not going to change the system.  I do not believe that violence toward law enforcement officers is justified in any circumstance, but, I also know of many instances when law officers have acted in a manner to cause their actions to become unlawful.  The lawfulness of a persons actions only becomes clear in a court of law.

 People have a right to ask what authority the law enforcement person is using when they seek to do something (like conduct a search on someone, enter a house etc) and what grounds they use to base their decision.  Once these questions are answered, even if the person doesn't agree with the answer, the actions of the law enforcement person would then be deamed lawful, until tested in court.