Law enforcement works on behalf of the government. The government is to serve the people. If the people cannot trust law enforcement, people cannot trust their government.
Because individuals in law enforcement represent their government, and the people, they must be held to the highest standards. It should be considered treasonous to abuse this power, as it has both short-term and long-term repercussions for the community in question, and the nation as a whole.
People who seek employment in law enforcement must do so based on their concern for the public good, and not their ability to thuggishly oppress and control others. The police force is not a mafia, or a military.
If the people cannot trust the enforces of the law, then they cannot trust the authors of the law, or law itself.