in general regulations are aimed at "reducing opportunities for others to do me harm." and also providing non violent forms of recourse when they do.
As a consumer, you have to take measures to protect yourself regardless of whether you are purchasing goods and services from licensed, regulated providers or from some guy at the flea market.
Do you really have to take the same measures in both cases? Do you worry about meeting in public and bad checks when you do business with regulated sellers?
So people never get ripped off by businesses in regulated industries?
I'm sure I never made that claim. When they do regulations provide you recourse, you hear all those stories because people get busted and/or sued breaking the regulations. The American health industry provides a great example of how government subsidies lead to all sorts of market failures, that's a whole different discussion.
"The police have nothing to do with the rate of Craigslist transactions that end in rape or murder "
I disagree, when they bust a serial craigslist murderer or rapist they prevent those people from raping and murdering more craigslist users. That reduces the rate of craigslist rapes and murders. Without the police those people would continue to rape and murder craigslist users. The police also warn people about craigslist rapists murderers, robbers and scammers who are still on the loose which has to help as well. I am sure I never said that the main benefit of the police would be stopping crimes in progress. You really think there is zero deterrent effect from police and courts? I sure would hurt a lot more people without the threat of legal sanctions. I sure would have been ripped off more without the threat of taking people to court. Without courts what recourse is there?
"There is no reason why court arbitration services and security services such as are currently provided (badly) by the state couldn't also be provided by a competitive market."
There is and this is where anarchists often go into denial, the only reason anyone ever agrees to arbitration is because otherwise they would have to go to court and there are costs associated with that. Without the threat of court why would anyone agree to participate in your arbitration?
As far as competing security services we have many real life examples of that. We can see how that goes in real life anywhere the state has failed in its role as dominant protection agency. These "security services" are called cartels, street gangs and the mafia depending where you are at. That is the reality of life without a properly functioning dominant protection agency.
Prohibition is the abdication of regulation.