It's very much like if a cop discovers an unlicensed street vendor selling hot dogs and, instead of busting him, he takes a free lunch whenever he's hungry.
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Yea, I can see where you might say this. There's a lot in common between stealing a hot dog from a street vendor and forcing a person to submit to your sexual demands with a threat of jail. I guess the notion of a crime against a person is no different that the theft of a hot dog.
In your view, clearly, a prostitute, cannot, by definiton, be raped.
When she's actively offering it for sale, she cannot be raped. Kidnapped, extorted, robbed, falsely imprisoned, attacked, battered, beaten, etc., yes. Raped, no.
Just to be clear, I'm suggesting she forfeits any special sanctity accorded to that part of her personhood when she's actively offering it for sale.
During that time, although rape is impossible, many other "crime[s] against a person" are possible.