[apologies if the thread has moved on... I've been writing this one with a lot of baby interruptions!]
Sorry SGB, I don't want to seem like I'm targeting you, but I disagree with this: "I think the only way you could consider sex with robots to be 'worse' than sex with unwilling sex workers (ie those who have been coerced into the trade) would be if you deep-down believe that sexual pleasure should be restricted, and that it shouldn't be 'too easy' to obtain gratification."
I think you are trying to force the subject into two camps. Either 'all sex is dirty, bad, wrong and should be stopped' or 'all sex is great, everyone is entitled to do whatever they want, wa-hey!'. But neither of those is really true. The first is just the remnants of the myths of religious patriarchy and the hatred of women and women's sexuality, fertility, and expression - original sin and all that. The second is the sexual myth of capitalist patriarchy that is currently being promoted- which is essentially about all men having a right to unrestricted access to women and calling it healthy, real vital masculinity (and usually by implication - something that women 'consent to').
The first is wrong, obviously and doesn't need any explaining, but with the second, unfortunately 'all sex is good' is not a great adage since a turn-on for some includes sadism, torture, abuse of power, rape, instilling fear, controlling another, humiliating another, etc. The fulfilment of this darker, violent abusive side of sexuality requires the abuse or exploitation of another's vulnerability: either people with less relative power as individuals (eg having inadequate sense of boundary or healthy relationships through childhood neglect) or a group (eg -women as a class by men as a class).
So as to "I think the only way you could consider sex with robots to be 'worse' than sex with unwilling sex workers would be if you deep-down believe that sexual pleasure should be restricted, and that it shouldn't be 'too easy' to obtain gratification. - I disagree with this mis-characterisation of the OP because it is possible to have a wider analysis of the power-relationships within the status quo and to have concerns that men having their desire to impose their sexual will (instead of negotiate a mutual sexual gratification) given increasing license and resources, might possibly have an negative impact upon women in unimagined ways.