I think a big part of the problem is that people generally aren't good at judging the value of other's contributions unless they are working directly with them

I think a big part of the problem is that people generally aren't good at judging the value of other's contributions unless they are working directly with them or managing them (and even then, hit or miss). Having salaries be completely open invites comparison even when there is a lack of information. Bob the Developer in XYZ team makes 20k more than me, is that fair? Maybe, but I don't really know, and I can see that creating friction with the right (wrong?) personalities.