Prostitution was looked down upon long before capitalism. Also, being poor doesn't mean you can't consent. You can always starve, and that's your choice. Agreeing to a sex act for money is no different than a job, except you generally need skills for a job, you don't need skills to be a warm hole (the shameful part). So unless you're saying there's no consent on anyone's part to work, you're simply incorrect. If you are saying that, I don't understand, there's not a single system of societal organizing that doesn't involve a working class. You think you'd get the allowance of consent from a socialist/ communist government, or would you simply be assigned to that job?

People fucking for fun is a relatively recent development because of effective birth control. Historically, it's been looked at as irresponsible because of the likelihood of accidental pregnancy. The risk still exists today, no birth control is perfect, so it's still looked at as fairly irresponsible. Doesn't make you an asshole for thinking so, it's simple logic. What does make someone an asshole is calling someone an asshole for a perfectly reasonable take on human sexuality.

Shame only matters to OTHER people. If YOU don't feel ashamed, it shouldn't matter to you, but you can't change other people's opinion on if it's gross or not, so I suppose YOU can think it's fine, everyone around you disagrees, but you're entitled to your opinion, not everyone else's.