The reason why socialist societies exists, is that pure libertarianism usually leads to a very unjust societies, with powerful individuals and a lot of exploitation.
Because socialist societies are a model of justice, maybe? You're either naïve or oversimplifying.
With justice I mean the agreed price for cooperation.
In a libertarian environment the price for cooperation is determined similar to the free market, supply and demand. However there is no limit on what two parties can agree upon. And if one party achieves monopoly on a certain cooperation item it can exploit its bargaining position (and usually does). This is a self-enforcing loop: a powerful entity becomes more powerful with time.
In socialists environments the price of cooperation is usually determined or enforced through different means, or at least capped. But the problem is that there is no better tool than the free market for price discovery, even for the price of cooperation. That's why any price determined by socialists usually leads to inefficiency.
I find the tax system we have represents a compromise: You need free market mechanisms to implement price discovery for cooperation (products, jobs, etc...) but at the same time you want to prevent the formation of monopolies and extreme bargaining powers.