As I've said in previous discussions about #talkpay, it only hurts your negotiating power as an employee. Even if you are a better at negotiating than your co-worker, they aren't going to care, which will hurt morale.

All Tax records and salaries are public information in Sweden and Denmark and it doesn't mean you, as an individual will get paid more. It means you get paid at exactly your market rate, which tends to be less. It's great for the person that doesn't want to work on their negotiating skills, but bad for the person that does. Some people are also worth more as an employee (IE: better skillset, more experience, etc), but the person making less will most likely not see this.

Privacy is one of the only things as an individual that gives you power over a big company during negotiations. Why in the world would you ever just give this up?

I never talk about my pay. I run a business now and won't divulge this information to anyone. Many people are jealous by by nature and when they know for sure you are doing better than them, will bad mouth you, spread rumors, and do anything in their power to hurt you. I've seen it in my personal life and I see it every day on Twitter.