People recognize there exists, to some extent, a moral obligation to do work. But if we accept prostitution as "just another job", aren't we implying that people come under some measure of moral obligation to accept that job if it's the only job available?

For instance, people may lose unemployment benefits if they turn down a "suitable" job. I cannot imagine anyone would want to extend this rule to prostitution.

I can imagine people who would, if only tacitly.

It's not news in the UK that one of the side effects of tuition fees has been a big increase in student-age women funding their courses by selling sex.

You can argue whether this was an intended or unintended consequence.

But for anyone buying, it's hard to argue that increasing supply and lowering prices isn't a happy result.

I don't accept that there is a moral obligation to do work (in the sense of a paid job). Work is a practical economic necessity for lots of people, and it may be instrumentally necessary to some other moral obligations, but it's not one in itself. And, insofar as work is an instrumental necessity to other moral obligations or a practical necessity for survival, the type of work one is able to do being outlawed doesn't make it any less of those things (though it may make one's life much worse.)

Can men loose unemployment benefits by refusing a military job? In an ideal world, you could object both prostitution and military jobs by saying you find them immoral ("conscientious objector").

Social mores are full of exceptions. Killing as murder vs. self-defense vs. getting an abortion, for example. I don't see any reason why prostitution couldn't be lumped in with other exceptions.