Contracts date back a thousand years, contract law is much newer.  Things can exist without laws.  Laws are a violent means that the ruling class uses to inflict norms on society.  Don't buy the hype, people can behave well without laws.  A contract is just a written agreement between two parties, you don't need cops to shake hands.  I suspect that you're more concerned about torts, contract violations.  Here's a suggestion, the BTC community needs a professional arbitration service.  Call it "For Profit Justice".  When there's a dispute between two contractually bound parties, a neutral arbiter can determine the extent of the violation, decide on a restitution, and rule in favor of one party or the other.  That business can then publish a list of all individuals that have breached a contract and failed to make restitution.  That way, anyone planning to transact with another BTC user can consult the "Dishonest List" to check the credibility of the other party.  Additionally, there can be an arbitration fee.  Then, there will be competing arbitration firms and sound contract enforcement, without state violence.  I know it's hard to see things in free market terms, but I believe we can do it.