People just need to look at the actual history of socialist countries. The more socialist, typically, the less free their people and the less economically successful they have been (and by "less economically successful," I mean subject to famine, etc.). Not coincidences.
Modern socialists want to disown these countries, of course, and say that they were never really "socialist" to begin with. That's the way to preserve the idea that their theories might still pan out, in some fuzzy utopian future. But in reality, on planet Earth, socialism has been an abject failure.
Modern countries that have features of both socialism and capitalism -- "mixed economies" -- are often successful, but if someone wanted to understand the engine which drives that success, they would be advised again to study the comparative history of socialist economies versus capitalist economies. Social science is "soft," perhaps, because we cannot go to the laboratory to settle disagreements, but in my opinion, the historical evidence for the failure of socialism both exists and is clear.
