When your scope is Europe ... The US is not the exception in the world, it's Europe which is.
The US has a dynamic job market where it's easy to lose your job, but easy to find another one. In Europe, and that's true for most EU countries, it's really hard to lose your job, but it's also really hard to get one for the very reason it's hard to get fired - and when you get a job, you will have to compromise on compensation and other benefits. It's not black and white here. While the European market is appealing to some people, the US market is preferable to others.
But that made me curious, and answering my own question, it's this guy https://en.wikipedia.org/wiki/Peter_Hummelgaard who is indeed a Social Democrat .. So much about workers rights, funny ...
Re-reading your comment again, I'm not sure that I understand it: "Let's see whether Denmark remains competitive." What do you mean?
I agree with that, it's a very individual topic. I'd say for high paying "high performance" jobs the US model definitely has an advantage but for low-wage jobs it's quite the opposite.
In MANY other countries there is already WAY more regulations regarding layoffs and firing employees that has nothing to do with unions.
In Germany there is a probationary period in which you can just fire somebody for no reason basically. That time can be like half a year (in my case) and in most cases it becomes clear if the new hire fits your team or doesn't.
All unrelated to unions though. The big unions in Germany for example have a lot of power and if you are just a simple welder for example you'd have no chance getting anything done without a union.