IMO, companies should not be allowed to keep salaries private but I do think employees should be able to keep their own salaries private. I don't want coworkers or the public to know my income for all sorts of reasons. It's just not anyone else's business.

This whole notion that the only way for someone who thinks they aren't paid enough to get a raise is to know everyone else's salary and then use that as leverage is absurd. If you feel like you aren't paid enough ask for a raise and explain why you feel that way. If you're turned down look for a different job that values you at a level you're comfortable with. If you still can't make the amount you desire maybe then it is time to check your own assumptions and see what you can do to provide more value so that you can get it in return.