I'm not sure where I stand on it.

I wonder if it could end up with everyone being paid a lot less:

"oh, this guy is asking for a salary increase. Does this mean I need to give the entire team a salary increase so no one feels bad?"

It may end up that employers become more strict as to what you earn in a given role to avoid people losing morale when they see their not earning as much as a colleague, which could limit earning potential for some people.

I'm earning more than I ought to be because I negotiated it. I think that would be unlikely to happen when everyone's salaries are transparent. It's probably good for everyone else, but bad for me.

There's also the issue that people assume they are doing the same work as a colleague just because they are doing the same job. This is rarely the case. Things like initiative, an eagerness to get involved in new things, friendliness, trustworthyness, negotiation skills, how long you've worked at the company etc all will make a difference to your salary - and may result in you getting paid more for the same work.

Yet these are things a lot of managers might struggle to explain to someone complaining that their colleague earns more than them.