Libertarian ideology is based on the classical liberal tradition that each person has the a priori right to life, liberty, and property. Since you have these rights, you may dispose of your person and property as you see fit as long as you do not infringe upon these rights of another. This leads to the non-aggression principle, which in bumper sticker form is "don't hurt people and don't take their stuff." Basically, the initiation of violence is prohibited unless it is in defense of property or as punishment for a crime.

All individuals in society should be treated equally under the law, including members of law enforcement and others within the government. If I am not allowed to commit violence against you until you have been convicted of a crime, neither should anyone else, whether or not they wear a police uniform. Indeed, libertarianism advocates for private, rather than public, police forces.

> what is the ideology that lacks them

Statism in all forms grants special privilege to members of the government, including the power to tax and hold monopoly on the use of force. The US criminal code is full of exceptions for on-duty police officers, judges, and others, especially regarding firearms laws. Police officers can carry firearms into school buildings where others are guilty of a felony if they do, for instance. Thus you have inequality under the law. Such police immunity is what leads to the abuses we see every day.