It’s generally recognized (at least in the United States) that limiting the potential for abuse by the government or agents of the government is more important than limiting other forms of abuse. A person has a variety of forms of recourse against non-governmental abuse (including appealing to the government), but the only recourse against abuse by the government is violent revolution. Even when raising a formal complaint against the government, it is the government that adjudicates whether the government’s behavior was abusive. So it is essential, even if it causes other negative side effects, that the government not be able to abuse people in secret, or in ways that it can later deny occurred.
> Another thing, what happens to the people who don't have a lawyer or whose friends and family don't have the resources to take on the police department in the event that the police detain and abuse them? Who would they be able to call in that situation to seek justice if the same police who committed the crime are receiving the call?
In theory, assuming the police don’t entirely disappear someone, they will eventually be released or have to be tried in court. In either case they would then be in a position to report local police misconduct to either a regional authority like a county sheriff, or to the FBI, which has a general mandate to investigate abuses of people’s rights.
In practice, the rule of law can be thin on the ground outside of metropolitan areas. Police departments are small and tight-knit, judges are extremely friendly with the police, juries are extremely likely to rubber-stamp whatever charges local police want to happen, and police and prosecution are likely to “forget” about a wide variety of standards and public disclosure requirements.