I started catching my ass up on Dollhouse, because I'm a dork like that. I am not really up on the reviews, but the ones I've read have been fairly negative, non-committal at best. My impression is that reviewers were expecting a little more of a specific condemnation of the prostitution-like aspects of the Dollhouse business model. Not perceiving it, they conclude that the show condones prostitution, or exploits it for the audience's titillation.
The criticism is partially correct in that, at least so far, Dollhouse has refrained from a portrayal of the sexual exploitation of the "Actives" as uniquely immoral. Which is not to say that their situation is shown as anything other than horrific. But the horror stems from denying them their personalities and memories, with sexual exploitation being merely a facet of their dehumanization: brainwashing someone into a willing assassin is as violent an act as brainwashing her into a prostitute. Viewers and reviewers who want the sexual abuse identified as especially heinous violations are missing the point.
This is a theme that Joss had begun exploring in the final televised season of Buffy, where the expectations of the duties of the Slayer, imposed from without upon a young woman without her consent, echo the expectations society has for all women from the day they are born. Dollhouse extends the (uncontroversial) theme of women's ownership of their own bodies along the lines of feminism's broader critique of capitalism, with the idea that all humans should have a right to their own minds as well.
Flashbacks have hinted that Echo, at least, began working for Dollhouse willingly, though doubtless with the understanding that she had no other viable options given her circumstances (still unknown). The horror of her employment's reality makes clear that such a selling of one's soul is illegitimate in its essence, and does violence to the subject's humanity.
Others participating in Echo's dehumanization are tainted and dehumanized as well, as demonstrated by the head of security's obvious contempt for the Actives. Even a sympathetic character, like Echo's Watcherhandler Langton, is faced with the impossible choice of either abandoning his charge to a potentially less caring successor or staying to lend legitimacy to the enterprise. In this way capitalism sorts everyone into those who are irrelevant and those who are complicit, the only other option being (going out on a limb here in a prediction for where the narrative's headed) to bring down the system itself.
Anyway, I expect that reviewers who find themselves turned off by the value system implied by Dollhouse are picking up on two quite real themes: an absence of any specific objection to sexual prostitution in the context of more general and horrifying violence, and tension resulting from trying to square feminist-humanist values with the inhuman excesses of capitalism. A reviewer operating from a worldview in which sexual violence is uniquely vile, not because of its denial of humanity, but because of its power to sully and impart shame on its victims; and in which capitalism is a force of individual freedom rather than its enemy; is going to be understandably disconcerted by a narrative that does not share or opposes those values.