Libertarianism is a political philosophy strictly concerned with forming a legal theory of when the use of violence is just and moral or when it is criminal. It is criminal when it is aggressive violence; when violence was initiated against a person or their property without their consent. It is moral when it is defensive violence; when it's used to repel invasions of one's property rights.
Libertarianism is not opposed to violence, but is opposed to aggression as defined above: violence that is not used in the defense of property rights, but to infringe upon those property rights. We anarchist-libertarians logically conclude that there is never a time when this aggression may be deemed morally just, and therefore we oppose all of the State, as all statism rests on aggression.
We term this: The Non-Aggression Principle
As far as rights are concerned, it is necessarily our right as self-owners of our bodies to be free from aggression; a right to non-aggression. No one has a right to use aggression against someone to provide themselves with something, and even if they're powerful enough to do it, receiving approval though the democracy, then it still doesn't make this action moral. Rights, then, are rights to property that is voluntarily contracted, i.e., acquired in a way that infringed on no one else's contractual claims to property: trade, original appropriation, etc.
Although almost no one wishes for the purpose of the State to be the preservation of our natural rights anymore, were it even capable of doing so, but rather for it's ability to implement socialism, i.e., positive rights to others' property in the form of redistribution and "public property", experiments in "limited-government", an idea supposed to protect property rights and enforce contracts, are an empirical failure. It didn't do it and it grew into what it has become today. I believe the best way to achieve protection of our [property] rights will be with no government at all.
Since the State must come into existence violating these rights, it cannot be expected to protect them, and must be seen as the great violator of rights. It is fallacious to assume rights cannot be protected without government, because they most certainly are not with one. We contend that property can be protected by voluntary agreement, i.e., entering into associations with firms dedicated to preserving one's property rights: private arbitration, private insurance, private security, etc. That, or do it yourself: self-defense. For economic reasons of the division of labor, it's likely the specialization of such a service would be delegated to various competing companies in the same way that no one wishes to entirely grow their own food. The garden may supplement just as the gun would, but might be insufficient.
A right, then, in this negative sense, means that you have the right to have people not do things to you; not that you have a right for other people to do things for you. My right to ingest marijuana is just that: a right to ingest it; to have no one prevent me from doing so. It is not a right to be provided with marijuana. A "right to birth control" should mean the same thing: that no one has a right to ban it, i.e., prevent you from taking it; it shouldn't mean that someone else doesn't have a right to not give up their property now in providing you with "free" birth control. Ending the forced transfer of property to provide birth control to people should, in our view, be seen as a good thing: rights to not give up your property against your will are being reestablished, not to mention opposition to this for moral or religious reasons. Progressives, on the other hand, would see it as a reversal of freedom. But they hold the wrong concept of rights, which they consider to be a right to use aggression against others in order to make themselves recipients of property.
Whereas the libertarian would see the "right to health care" to be the freedom of choice and association with which ever health providers you wished, without being forced to choose one monopolistic provider, the single-payer State, they would see it to the contrary: a "right" to health care means that you have a right to be provided with it. With the State—a monopoly one whatever services it takes unto itself—there is no freedom of association. One is not free, i.e., having the right, to decide who they associate with; they're forced to associate with the State that aggresses against them and there is no freedom of contract of exchange.
If "rights" were positive, meaning they require the positive action of someone else, then this would mean that not everyone has rights. Some have no rights at all: the doctors forced to provide the service, the taxpayers forced to hand over their property, etc. Some would have to do things for people instead of refrain from doing things to them.
Therefore, the only crimes are violations of property rights. Anything that is not a violation of property rights, such as drug use, prostitution, gay sex, cursing, infidelity, speeding, gambling, tax evasion, where there is no victim, is not a crime.
What we believe in theory isn't a reality: the State creates a perverse understanding of justice and rights, and very much so subjugates us into following their way. But this doesn't change what we hold to be true philosophically, that: It is our natural right to be free from uninvited aggression, and it's statism that is inherently criminal.