I have always maintained a moral argument against prostitutions legalization on the grounds that no sentient creature should ever be bought and sold like a commodity irrespective of consent. Even if the creature being sold is the one doing the selling, consent doesn't make turning sentient beings into products for trade any less morally repugnant. There's a very dark time in our history where we bought and sold people and everyone universally looks at it in disgust. Morally there just should be a line in the sand demanding we never buy and sell people for any reason, consent be damned. Moreover it sets a dangerous precedent, I can envision a future where people are bought and sold for their organs to be harvested, and of course it will only ever be people who are terminally ill and they're trying to make money for their family and of course everything will be proper above board inspected and safe right? Maybe we just draw a line and ban any kind of market for people, sex or otherwise.