Revulsion against sex work isn't unique to female prostitutes. We're also repulsed by men who sell themselves to women, even though there's a general cultural assumption that a healthy man wants to have sex with nearly every female he sees. Something about sex work violates a deep belief--whether cultural or hard wired I don't know--that sex should only be traded for affection.
But if the only prostitutes were men selling themselves to women, no one would want to make it illegal. Supporting yourself that way might bring social opprobrium, like becoming a Morris dancer or eating live chickens--can't you find something better to do? But we wouldn't criminalize it in the name of protecting them from violence, criminals, or the untold horrors of multiple anonymous sexual encounters.
Um ... I would still want to make it illegal. I wouldn't want to make it illegal in the name of protecting gigolos from violence or unprotected sex, but then again, that's not fundamentally why I think female prostitution should be illegal either. I think the "protecting vulnerable women" case against legalizing sex work is a perfectly reasonable supplemental argument for keeping the ban in place, but ultimately the case for the ban stands or falls on one's view of morals legislation: First, whether it's appropriate for the law to restrain people from activities that are freely chosen but ultimately self-abusive and morally degrading, and second, whether prostitution, female and male alike, is sufficiently self-abusive and degrading to warrant legal sanction.
Pace Glenn Greenwald, I suspect that a great many people in the United States would answer yes to both questions. But based on the response to the Spitzer case (and the Vitter case before it), it appears that nearly the entire liberal (and libertarian, though that's to be expected) intelligentsia would answer no the first, and dismiss the second as an irrelevancy.
Hence the search, among those liberals leery about making sex work legal, for arguments that suggest that all prostitution is essentially non-consensual - that it's too exploitative by its very nature to count as something "consenting adults" should be allowed to do. But the evidence they muster tends to depend on a pre-existing moral bias against making prostitution legal. For instance:
... most women in prostitution, including those working for escort services, have been sexually abused as children, studies show. Incest sets young women up for prostitution — by letting them know what they’re worth and what’s expected of them. Other forces that channel women into escort prostitution are economic hardship and racism.
All true - but the obvious pro-legalization rejoinder is that being sexually abused as a child, or being born poor and black in inner-city Baltimore, pushes people toward all kinds of life choices that we don't choose to regulate. We don't forbid women who were molested by their fathers from dating older men who treat them unkindly and use them for sex, and we don't make it illegal for poor women to work unpleasant jobs cleaning houses or serving food at McDonalds. It only makes sense to ban prostitution if it's in the same moral/legal category as incest itself, rather than being akin to the kind of run-of-the-mill exploitative relationship that incest might incline a woman (or man) toward later in life. Which is to say, laws against prostitution ultimately depend on the assumption that the state has an interest in preventing serious forms of self-abuse, and that renting out your body to satisfy another person's sexual needs is a form of self-inflicted violence serious enough to merit legal sanction irrespective of why and how you decided to become a prostitute in the first place.
I should note that taking this position, as I do, doesn't preclude supporting changes in how we enforce prostitution laws - by targeting johns and pimps, say, and letting streetwalkers off with a slap on the wrist - any more than my belief that crack cocaine ought to be illegal means that I wholeheartedly support the war on drugs. The view that the law should be a moral teacher where certain forms of conduct are concerned leaves one with plenty of latitude for making prudential decisions about how and where that teaching should be carried out.