Every gun collecting, gadsen flag waving self-described "libertarian" I have met in real life, curiously, also sported things like thin blue line stickers on their pickup truck and was a huge supporter of their local sheriffs department.
Who decides how a disagreement gets resolved? Even if you do contractual everything, what happens if a contract dispute arises? Sometimes contracts are done based on misunderstandings, or someone tries to press an advantage in a way the other party doesn't like.
Beyond all that, the "if you believe in letting everyone exercise rights as long as they don't infringe on someone else's rights" sounds a lot like the wishful thinking that goes along with advocating communism. If everyone believes in from each according to ability, and to each according to need, you don't need legal systems and law enforcement, either.
One can take any large-change political idea - communism, libertarian, anarchist whatever - won't there be a transition? Does even the most hardcore supporter believe you can upend society in a day? That seems straw manning a true Scotsman to me - where if you don't support the sudden, radical change of society you are not a true Scotsman.
You can run the experiment yourself. Sh/would a communist see private land ownership as the first thing to go? Or sh/would it nationalize business? Sh/would a libertarian want police gone first? Or licensing for lawn cutting?
I respect the job the police do, and I wouldn't want to have to do it myself. But that is completely orthogonal to holding individual police officers accountable under the same laws as everybody else. Agents of the state summarily executing people is one of the most egregious violations of individual liberty possible - larger than "licensing for lawn cutting" or most anything else. The "thin blue line" flag is a counter protest to the call for police accountability, and it is blatantly hypocritical to call yourself a libertarian while opposing a major libertarian critique.
https://www.lp.org/issues/crime-and-justice/
https://old.reddit.com/r/Libertarian/search?q=Police&restric...