Personally: I've reached the point where I don't want to know what my colleagues make. I know many of them make significantly more, but that's fine. In some cases I'm outright happy for them.
Yes you are exploited if you don’t know what would be possible.
Here’s an analogy. Say I wait tables at a restaurant. If I discover my boss has been skimming off my tips, I’m going to be upset — even if I was perfectly happy with my pay before I learned that.
If salaries are public it isn't a super rare case where friendly coworkers will help to build you up to asking for that promotion.
I agree with this 90%. More information is very useful most of the time, as long as it is high quality.
However, given that we humans do not have infinite processing power or infinite emotional capacity, there are obviously limits to the amount of information we want to have at any point in time. And these limits will change depending on the situation and our own internal state.