It's all about consensus and enforcement. The courts hold power because we all agree (actively or passively) that the decisions made by the courts are legitimat

It's all about consensus and enforcement. The courts hold power because we all agree (actively or passively) that the decisions made by the courts are legitimate. We choose to keep our citizenships and pay taxes to enforce these decisions with coercive/violent means (police). If people lose faith in this arrangement and start disregarding the legal systems - e.g. if the police refuse to do their job - you could very well end up with blockchain officers taking their place and kicking down doors with the approval of the masses. For now, though, it doesn't really matter what you own on the blockchain because you have no shotgun to back it up (no legitimacy nor means of enforcement).