A voluntaryist libertarian believes that all adult relationships should be voluntary.

A voluntary society is what results when you apply the Zero Aggression Principle (the ZAP) consistently. This means that institutions of governance must be…

Voluntarily funded (no taxes)

Open to competition (no legal monopolies)

The result is something we call consumer-controlled governance. In other words, citizens should have the power to withhold funding or to choose another service provider.

Some libertarians disagree. They make exceptions to the Zero Aggression Principle. They argue that some legitimate government functions, such as police, courts, national defense, and pollution control, require taxation, though they still hope to limit those functions and taxes.

Source: What is a Voluntaryist? – Zero Aggression Project