The wrongness of prostitution is less about personal choice as much as the structural pressures that place people into positions that make it their only rational choice. It's not explicitly sexual violence, but in many many cases it is implicitly a kind of unjust situational oppression. For every "high class" prostitute (usually white and in the first world) there are far more who have no power to negotiate and are broken and dependent. So when people talk about the "choice", it's frustrating because the majority of this work is in fact not like that, and gets forgotten in favor of the maybe 1% of prostitutes who have a decent amount of control.
It's also about dominant cultural norms. Sexuality is powerful and a valuable source of human impulse and motivational sentiments. If people throw their hands in the air and say "who cares? sex is just sex! pleasure is just pleasure! no choice of how to use it is better than another." then we are essentially saying having any sexual culture at all is invalid. If a community seeks to have a unity of values and moral sentiments, then seeking some degree of consensus on the better and worse ways of behaving is rational. Prostitution, assuming communities work to provide space for more moral means of sustenance, can be said to be inappropriate and worthy of disapprobation. That's different from saying there is a positive obligation to refrain from that behavior. Imagine your child grows up and becomes a prostitute. I think it would be reasonable for you to disapprove, and to emphasize that it does not meet your standard for sexual values and boundaries. And it's not just your personal opinion, its a cultural orientation that rationally places a certain set of vulnerable and intimate activities beyond the realm of markets. Some sorts of things ought not be for sale. Assuming the activity is decriminalized, it's not wrong for people to express their disapproval and to discourage the choice.