...we do it this way because we do it this way because that identifies us as us.
That's the opposite of critical thinking.
I'd say it's orthogonal instead. But critical thinking, in the admirable form, seems to be a learned skill. What I'm describing is an emergent property of human behavior. My critical thinking ability tells me I might do well to appreciate humans for what they are and what they produce, rather than for how I might prefer them to be.
I also think there's a certain value in this kind of mindless, undirected evolution of societal norms. My culture gives me standards, no matter how arbitrary, I can measure myself against - a way to determine my own worth in a larger context. Nature, as far as I can tell, doesn't do this for me. There is no calculation in physics I might use to justify legal or illegal prostitution. It really is humans all the way down.
If I accept that disgust and aversion are real phenomenon with a valid evolutionary mechanism (don't eat that, it stinks), and I note the feelings are transferred to acts like prostitution (or as Cecil Adams put it, "Icky") am I not just recognizing a fact about human beings, that we are at least partially driven by unthinking emotional reaction?
The challenge then, for those who would like to see prostitution legalized, is to reframe it to make it palatable. Arguably, this is what regulations do where prostitution is legal. It isn't a free-for-all, it's still illegal in some forms, but the regulations have the effect of removing some of the taint. Some types of prostitution are still illegal in New Zealand. According to Wiki: "It remains a crime to coerce 'someone to provide sexual services'. Sex work is also prohibited for those on temporary visas, and immigration for and investment in sex work is prohibited."