There are many, many problems with these stories. The first and essential problem is with the premise itself. "Artificial" people, created only for the sexual enjoyment of others.
The idea of any people being "artificial" is a can of worms itself. It's one thing to talk about a small robot going around vacuuming your carpet and another to talk about robots for sex, a very intimate act (at least, as it is considered to be by many). So you're already dehumanizing sex. Even separating sex from life, sex being something only living organisms do and something which propagates life.
Next, these robots, unlike life-like sex dolls, invariably have human feelings and thoughts and emotions and ethics, and so on... they're people. Not sex toys. They're people that the authors are dehumanizing.
Sex workers are dehumanized as it is, in real life. You have to start unpacking the way the stigma against sex workers works in the real world in order to get at this angle of the problem. A story in which the sex workers are robots or androids (but amazingly, have much of the range of human emotion etc. etc.) just takes this stigma and makes it literal, i.e. "These characters aren't 'real' people, so everything that's going on here is completely OK," at least below the surface conflicts. You never have to get into the deeper social and economic issues that drive people into sex work, you never have to address human-on-human exploitation, or drug use, or STDs, or pregnancy, or lack of education, or abuse, or even the emotional impact of being forced into sex work -- anything at all, because these are androids. You can casually mention that they're being abused, and don't have to wrestle with that in your story because "these aren't real people" -- you can adopt a tone of just "oh poor androids, too bad they're being abused unspeakably!" /sniff/ Then the "bad guy" who does the abusing gets his comeuppance, and we're done. Yay! (Not.)
These androids have been made with the express purpose of being in sex work. It's OK for them to be doing this with themselves because that's what they were built to do. There's no guilt. That's what these entities were designed to do, and it's their most natural role! They were created for this purpose! Like, um, that argument about women being "created" for domestic work and people of color people being "created" for manual labor and um, all that other real life oppressive bullsh*t. In SF, it can be stipulated as part of a story's premise that 1) machines can be "made" for the purpose of doing certain things (we all accept this as part of society's master narrative), and 2) these machines can have thoughts and feelings and ethics (common SF premise). We can therefore get away with not considering these thinking, feeling, entities "human", and thus, we never have to address and challenge the underlying implication idea that people can be "made" (by some divinity, aliens, or other humans) to be exploited by others and limited in their social role to the place where the dominant group deems them "appropriate".
(As an aside, SF seems to do this with various other groups of people, even real-life groups, but that's beyond the scope of this essay.)
So now that we have some (sentient, feeling, intelligent, moral) "non-people" who were created by "real people" for sexual exploitation, and there's no guilt in any of this, we add in the race fail and gender fail and sexual orientation fail etc.. Sexbots can have "perfect" beauty no human female (or male) can achieve, thus actualizing the advertising industry's presentation of women as objects who can only achieve "perfect" beauty through genetics, starvation, surgery and digital "enhancement". On the race end of things, sexbots may be compared to or referred to as "geishas", or maybe they're default white and turn into PoC for some plot point. Or PoC bodies and skin colors may be referred to with reference to food. Or the sexbots may be said to have no race because they can turn into any race (racial identity thus being reduced to ("artificial") skin color, facial features and hair features). This way, the sexbots can "be" any race that the person who owns or contracts them wants, fulfilling his/her racial fetishes (and without having to deal with any of the issues of objectifying, "othering" or exploiting "real" PoC)!
We also have have sexbots who "service" people of any gender (making them more "valuable" as commodities), and ones that can morph into having any combination of primary and secondary characteristics their owner desires (fulfilling all trans and intersex fetishes of their owners/those who contract for them), all without any discussion of the exploitation/dehumanization of trans folks in sex work in real life. These androids were designed and built for doing this and they're happy to do it! (In fact, the way they were designed, they really can't do anything else, or even imagine doing anything else! Your TV doesn't wake up wanting to be a microwave oven, now does it?)
Sexbots are also portrayed as "perfect" lovers because they can and will do anything, unlike real people, who have boundaries and preferences and who are capable of saying "no." Oh no, artificial people are programmed not to be able to say no! (Rape culture, anyone?) They always want sex, your way, all the time! You can always be sure no means yes with a sexbot. In fact, you can even abuse them with the most violent of fetishes, because they're not "real people". Even in stories where the sexbots don't like this treatment, and there's some sense of "the guy who treats his sexbot like this is the bad guy", the ethics of mistreating a sexbot never seem to match up to the same ethics of "mistreating" a "real" human. It feels more like that spin on slavery that is sometimes presented to (white) children: "The slave owners who beat their slaves were bad guys, but they weren't all like that -- some slave owners treated their slaves well!" Without, you know, examining how slavery itself is the problem.
(Except sexbots can't even think of doing something else with their lives unless they're "broken", because they were "made" to do that one thing and that's how they were "designed". By SF premise.)
Oh wait, what's that about only slaves who were "mentally ill" would ever think of running away?
(Don't forget to catch that bit about the "submissive state that it was intended for them to occupy" and how this all supposedly comes from the Bible (here, the word of the Divinity who created us all. It's Divine Intent!))
So. At the end of the day, all those people who are seen as less than fully human, especially in a sexual context (women, trans people, intersex people, sex workers, LGB people, slaves, etc.)? If instead of making them real people in the story, we do the exact same things to them but we make them into sexbots, we're done! Problem solved! It's all justified now. Now they're clearly "in their place" and it's clear they've been "created to be there" and they're clearly "not really human" and we can tell as problematic a story as we like!
And then how dare some editor or blogger point out that all we did was put lipstick on the proverbial pig?
Note: I have yet to see a disability-sexbot story, but it would fail hard for the same reasons already enumerated here. I have read stories where it would clearly be possible within the setup for sexbots (disability fetish!), but as yet I have not received such a story.