But what exactly is the difference between a freelance contract and an employee contract? You can work freelance for a company for several years? Aren't all the employee benefits just negotiable things that a freelancer could negotiate as well? I think in that wider sense everybody is a freelancer. Everybody has to decide for themselves what job to take on, and what compensation they get. Job security is also something that has a certain value.

You can maybe argue that some people are completely unable to make those decisions and society should just make the decisions for them ("you are going to be a plumber" and so on...). That line of thought quickly leads into weird philosophical territory, though (freedom, free will,...).