Ok will try to answer your question Cote - I hope this will be clear, I know what I want to say but it is quite tricky to put into words as is quite an abstract notion.
Another reason why what I want to say is hard to express is because we are all so used to, and accepting of, the current status quo.
It will help me to gather my thoughts, I think, to examine our starting point - the current status quo.
OK, so. Currently, the situation is one of patriarchy, male dominated society. One can argue the finer points, but most people can see that men have more power, status and privilege than women. Thereby we are starting out from a situation of inequality - one sex has a bigger slice of the capitalist pie than the other.
History has shown that when there is unequal status between groups of humans, the ones with the higher status develop a sense of entitlement, (white supremacy is a good example of this). The ones with the higher status are brought up to believe that they deserve this unearned privilege and that this is a natural and normal state of affairs. It kinda suits them to go along with this belief without too much questioning because it is nicer to be in the high status group. They do stuff like being benevolent and gallant towards the lower status group in order to make it a bit nicer for them too (white supremacy good example again).
The lower status group are also brought up to believe that this is a normal state of affairs. They are taught that the benevolence and gallantry are signs of the respect and admiration that the higher status group has for them (as opposed to patronising crumbs of manipulation from the table of power).
Both groups are encouraged to normalise and internalise all the above. All this stuff is reinforced, over generations, in a myriad of insidious ways. The higher status group have more power and get to set systems and hierarchies up to suit themselves and which reflect, reinforce and normalise the situation of unearned privilege. The lower status group are constantly told that this is normal, they internalise this message even though some of them have some sneaking doubts about this so called 'natural order'. Et voila - we have a status quo.
The lower status group generally have or can provide something the higher status group want or need - for example, labour in the case of white supremacy. In the situation of male dominance, there are various things the high status group want from the lower status group - one of these is sexual gratification and/or the opportunity to exert sexual power over them. The whole system of status is gendered, and therefore sexual power is a very powerful institutionalised tool (in addition to providing pleasurable orgasms).
This human/political aspect is what makes prostitution different from drugs or alcohol. The 'raw material' of prostitution is people, generally women and children. The raw material of drugs, alcohol and any other commodity is inanimate (although of course harm is done to people in the production of these commodities and the transformation of the raw material necessary).
The 'raw material' required to provide the 'service' of prostitution comes from the lower status group in our status quo. It is provided by the people who have fewer choices, less power and who are more vulnerable and more easily exploited and abused.
We can quibble over whether a prostitute is selling their body/access to their body/their bodily integrity/their consent/a sexual service, etc all we want. However the fact remains that people are required in order to commodify sexual intercourse. The sexual organs and sexuality of these people is commodified. I think most people who have any sense of empathy, can see how a punter penetrating a person is different to a punter using an inanimate male masturbater.
So back to Cote's questions.
Why do I think society condemning prostitution will change behaviour significantly when it doesn't with, say, drugs? Firstly, drugs are physically addictive in ways that orgasms aren't (I have no time for sex addicts). Secondly, orgasms will not be made illegal because prostitution is. Thirdly, sexual behaviour and sexual relations are hugely psychological and clearly influenced by culture and environment - just look at how different our own sex lives are to those of our grandmothers (my own mother never experienced oral sex in her 15 years of marriage despite having 2 children).
Finally (and this also answers the question about "The notion that prostitution will just continue underground is deeply offensive to men IMO") - I believe in the humanity of men. I believe that if society frowns on the sexual exploitation of one gender by another, and explains why that sexual exploitation is wrong, in a society where one sex has power than the other, that men as a group will listen and learn.
I believe that if you explain to men that civilised equal society will not accept sexual predation of the vulnerable, then men will respect that. If you continue to tell them that it is ok and not really exploitation because the vulnerable have 'chosen' to be vulnerable, lower status and exploited then men will continue to accept the status quo.
I think it is quite man hating to suggest otherwise - to suggest that if society educates its citizens to the harms and inherent injustices in prostitution, that men will carry on regardless. I think more of them than that.
If I were to be proven wrong then it would be proof to me that patriarchy is really women hating, that patriarchy spits on our freedom and on human integrity and justice and equality.
At that point I'll either call The Revolution or go off to live in a female only commune
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Apologies for essay of a post!