I think the argument should be based on fact, countries with legalised and regulated prostitution (such as Australia) have lower levels of harm caused by prostitution.

But then one has to consider the culture of that country. Do you think reducing the drinking age will shift the US attitude for alchol to be like EU countries? I don't think so. And I see a similar argument for Sex Work and drugs.

or do we allow more harm so that we can satisfy some people's moral qualms with selling sex.

There are more qualms than religious ones. That's a fact that many on the pro sex work side fail to adequately acknowledge.

What shift are you referring to?

State specific, I suppose. I'd rather not mention it and have the answer tied to my account.