I respectfully disagree with the OP. First, I highly doubt many expert economists will agree with the existence of extreme capitalism. Secondly, there is the fallacy of how things are during prohibition is how things will be without prohibition, that is to say there is the false assumption the action of prohibition does not alter the inherent constituent components of a prohibited act. Street hookers face controlling and abusive pimps, face potentially violent Johns, there are international kidnapping rings, substance abuse is rampant. As the argument goes, legalization would only further facilitate and encourage the perpetuators of these social ills by essentially hosting a fundraiser. Of course, however, the action of prohibition of any product will place it onto the black market of thugs with guns with dope, along with the absence of reasonable safeguards.
This same fallacy occurs with marijuana prohibition.
I also must disagree with Hooligan Harry's untaxability argument as it also commits the fallacy of how things are/will be. The black market is a cash market to avoid paper trails, so any product or service entering the black market will be paid in cash regardless of how would be the mainstream market. Secondly, if we look at somewhere as the Netherlands where prostitution is legal, tax revenues are thriving. Yes, indeed, there may be leaks of revenue which are unreported and evade taxes but this holds true for every business industry. I find the untaxability argument simply false.