How is that different from lifting boxes in some factory job, or whatever menial work?

I mean, I know the e.g. Christian answer.

What would the distinction be, however, without giving some special negative spiritual quality to having sex?

This person has a valid, subjective opinion on taking penis in return for cash, but it's not necessarily the case for everyone.

Note that I'm not saying that being a sex slave is better than working a low tier job. I'm comparing peeing in a bottle, having every movement tracked/optimized and skipping meals to deliver Amazon packages vs true freelance sex work.

Now, an actual fact, I knew a guy, a licensed accountant, about 20 years ago who did the accounts of a working lady (ok, prostitute). He said she was pulling in about £80,000/year. He didn't say whether she liked her job so I can't help you there.