If anything, violating contract laws should be far worse for them if they truly believe what they profess, since it is not the evil “guvment” which is imposing the conduct, but their own consent.
Additionally, Liberty consists of doing anything which does not harm others: thus, the exercise of the natural rights of each man has only those borders which assure other members of the society the enjoyment of these same rights. In other words, you cannot claim a right, such as property rights, without accepting the property rights of another.
Utopian political concepts, which Libertarianism and Anarchy are, tend to expect people to know the rules and follow them. They do not need a government to impose order. Instead, order comes from mutual agreement.
The reality is that the guarantee of the rights of man and citizens requires a public force. This force exists for the advantage of all and not for the particular utility of those in whom it is trusted. That force is exercised through the legal system and the proper use of authority.