Laws exist for five basic reasons, and all of them can be abused.
1. The Harm PrincipleLaws created under the Harm Principle are written to protect people from being harmed by others. Laws against violent crime and property crime fall into this category. Without basic Harm Principle laws, a society ultimately degenerates into despotism--the rule of the strong and violent over the weak and nonviolent. Harm Principle laws are essential, and every government on Earth has them.
2. The Parental PrincipleIn addition to laws intended to discourage people from harming each other, some laws are written to prohibit self-harm. Parental Principle laws include compulsory attendance laws for children, laws against neglect of children and vulnerable adults, and laws banning the possession of certain drugs. Some Parental Principle laws are essential to protect children and vulnerable adults, but even in those cases they can be oppressive if they are not narrowly written and sensibly enforced.
3. The Morality PrincipleSome laws are based not strictly on harm or self-harm concerns, but also on promoting the personal morality of the law's authors. These laws are usually, but not always, grounded in religious belief. Historically, most of these laws have something to do with sex--but some European laws against Holocaust denial and other forms of hate speech also appear to be motivated primarily by the Morality Principle.
4. The Donation PrincipleAll governments have laws granting goods or services of some kind to its citizens. When these laws are used to control behavior, however, they can give some people, groups, or organizations unfair advantages over others. Laws promoting specific religious beliefs, for example, are gifts that governments extend to religious groups in hopes of gaining their support. Laws punishing certain corporate practices are sometimes used to reward corporations that are in the government's good graces, and/or to punish corporations that are not. Some conservatives argue that many social service initiatives are Donation Principle laws intended to buy the support of low-income voters, who tend to vote Democratic.
5. The Statist PrincipleThe most dangerous laws are those intended to protect the government from harm, or to increase its power for its own sake. Some Statist Principle laws are necessary--laws against treason and espionage, for example, are essential to the stability of government. But Statist Principle laws can also be dangerous--laws restricting criticism of the government, such as flag burning laws that prohibit the desecration of symbols that remind people of the government, can easily lead to a politically oppressive society full of imprisoned dissidents and frightened citizens who are afraid to speak out.