> If somebody wouldn't have sex with you of their own volition, but is coerced into doing so for need of food and shelter, then how can it be consensual?
By that argument, wage labor is slavery just as much as prostitution is rape.
So, yeah, if you're that kind of socialist, there's a coherent argument for that point. But if you aren't, you may have trouble justifying why economic coercion overrides consent in one case but not the other.
Myself, I'm somewhere in the social democratic (US-style “democratic socialist”, perhaps, but not what that label would apply to outside of the US) range, and I agree that there is in fact an element of economic coercion in many but not all cases of work-for-pay in a capitalist economy (including, but not uniquely so, prostitution) which makes consent unclear in the general case and clearly absent in some specific cases, but that the best corrective is alleviating the fundamentally coercive nature of the system by improving the social safety net, not trying to ban the kind of work people are more likely to do only if economically coerced (which just leaves people either coerced into some other kind of work or, stuck in the conditions that they sought to escape by accepting distasteful work under duress, or—often—still coerced into exactly the same undesirable work, but without effective legal recourse for additional abuses in the working relationship.)