While I'm not against prostitution per se, pretending it should be considered a normal job is naive at best, disingenuous at worst. You're denying the suffering of millions of people around the world.
Just answer about this sincerely: would you want your sister or your mother work that kind of job? Just think about it carefully. If you answer yes, you're a liar.
And blah blah blah, "sexuality and romanticism aren't synonyms"... everyone here knows that. It's not as if anyone is denying that there can be sex without love and love without sex. It's an obvious strawman.
It's just that usually (not always), one leads to the other, not necessarily in that order. Pretending they are unrelated because there are some exceptions is dishonest.
No, prostitution is not a "normal job", because it involves a lot of psychological and physical factors that touch intimacy, social image and self-representation. I don't doubt there are well adjusted prostitutes, but I think they are the minority among the millions of exploited others.
Yes, any adult can choose to sell sexual services if they want to (emphasis on "they want to").
And no, this manga is just a fantasy and probably doesn't depict any reality about lesbian prostitution and it leaves the questions about that occupation unanswered, because it's not the focus of the story.
Part of the reason sex work is so unsafe in most of the world is because is because of it's illegality. When you decriminalize and regulate, as with any illegal industry e.g. marijuana, the criminal elements can be weeded out and it can be made as safe as any other industry. It's fine if you don't like it, but let's not pretend that this isn't just your personal preferences. Also, lets not ignore the tens of millions of people all over the world who are so uneducated about how to find a partner that prostitution is pretty much the only sexual intimacy they will receive in their entire lives. This is one of the biggest reasons that the sex industry will never go away. The vast majority of human beings, like all animals, need some kind of sexual relief that isn't just a hand.