It doesn't fight against tax evasion or anything, because the wealthy of the world will have yet another incentive to mask their income / assets through any of the number of mechanisms currently available.
If you want pay transparency to fight pay inequality, then anonymized pay based on role / job title should suffice.
Any legitimate need for such information can either be obtained through asking, or through the courts. At least then, I have a say in the matter and a right to defend myself in cases where I believe it necessary.
People are entitled to privacy. I wouldn't want random people knowing my salary anymore than I'd want them knowing what medications I take.