Watchtower's moral standards are abhorrent, there's many examples of that, but that doesn't mean people should have no moral standards. In general, "treat others as you would want to be treated" is a good one. There doesn't even need to be any theological component for that, Richard Dawkins and other biologists have written about how that sense of altruism and collective responsibility evolved in social animals (like us!) to help with the group's cohesion and survival - if everyone is only out for themselves with no regard for others' wellbeing, then the whole troop/herd/flock/colony/society collapses and they all die out, but if they work together, they all thrive.
Nobody wants to be sex trafficked and abused. So it's wrong to use prostitutes by that moral standard.
Lots of people's own personal moral standards would say that it's okay to do a lesser wrong for the greater good, like stealing to feed the poor or killing to defend yourself or someone else, and yeah, there's a lot of debate to be had there. But what possible justification could there be for sexual abuse? Nothing's gained from it that you can't get from just having a wank, and it does so much damage to the victim and keeps the whole trafficking industry going.