@Kolyo,
There is a big difference between medical ethics, and sexual ethics. I suppose you could argue that the issue is "charitable" ethics, but even so, medical ethics is different.
Removing a kidney is a medical procedure that involves a doctor (a profession bound by ethics) and a real risk of breaking an oath of the profession (first do no harm). Covering oneself in feces is a sexual fetish that some people do willingly for enjoyment.
I don't think you can compare the two.
[And still my main point that the moral failing in the hypothetical is the refusal to give help to the refugee (not the request for a sexual favor). Refusing to help period is just as immoral as refusing to help unless a sexual act is performed.]