Not necessarily, but it is probably the most common way it has been implemented in the US, and a potential downside depending on implementation.

Another downside is that it could release competitive information from private companies.

Sure, and the upside is a strengthened position as a prospective employee. As an employee or prospective employee to a new organization, what's the downside?

If you are currently underpaid, it could reduce you leverage with the prospective employer. I have 2Xed my pay because a new employer didn't know my current rate.

They still wouldn't know your rate. As I mentioned before, pay transparency isn't necessarily personally identifiable. Hypothetically you could've 4X'd your rate. Maybe your 2X rate is actually a lowball. Who's to say?

yeah, it really all comes down to implementation. How much information is available an to whom.

Being able to look up anyone by name in a public registry and see their exact salary would probably be a worst case This is the current state for public employees.

Anonymized data for companies larger than a certain size with job class (like levels.fyi[1]) would probably be a best case. However, if you want to get meaningful information about sex, race, age, & gender, this information quickly becomes identifiable for even moderate companies.

https://www.levels.fyi/?compare=Google,Facebook,Microsoft&tr...

Given the amount of tracking that's possible today, I think that anybody who cared would be able to easily determine your exact salary if the salary of every position at a company were published.