I did some research about 10 years ago (and every couple years do a recheck it for recency) and found that the more capitalistic an economy is, the higher long term standard of living growth rates for the poor. This is true empirically if you look both across various countries (even in poor parts of the world like Africa) as well as within the same country in different time periods.
Some governments have been successful at redistribution of wealth.. others have not. What is less intuitive is the vast majority of the time, substantial redistribution of wealth does in fact lower the standard of living growth for the rich, but it *also* lowers the standard of living growth of the poor as the temporary gains in forced redistribution are more than offset (over 10 year periods at least) by lower overall productivity growth leading to lower real wages for the poor.
Many (though not all) advocates of redistribution of wealth fail to consider the incredibly significant negative side effect of reducing long term productivity growth, and what impact that has on the poor. In other words, even if you succeed in reducing the top 25% wealthiest citizens from owning 80% of national wealth to say 50%, thus redistributing it to the poor, you have to also factor in the the pot of gold so to speak grows far less quickly. I've only be measuring for periods of 10 years or higher.. it is very possible that in the short term in some cases you can actually help the middle class. But I'm looking at it only from the point of view of long-term (sustainable) policies.
I will say the relationship between government and standard of living growth of the poor is not perfectly inverse (though extremely strong); Sweden is a definite outlier the last 20 years. They have a fairly large government with high redistribution of wealth and yet a reasonably decent growth rate of wages for the poor. I have some theories on it but am still investigating the details of that particular case. If anyone here is from Sweden and would be interested in sharing their thoughts that would be helpful.
My final thoughts are the United States is not the beacon of Capitalism it used to be (think: zero income tax; zero capital gains tax; zero estate taxes; zero dividend taxes; tiny other taxes including state/local for about 150 years.. compared to what we have now). Many people who argue against Capitalism use the US for comparison, when really we are only somewhat less socialistic than most European countries. In addition, it is helpful to factor in not only absolute levels but also relative change. For example, China is still more socialist than the US, however its delta of change is very high the last 20 years as they have gone from Communism to a Mixed Economy.. that is quite a change in a relatively short period.
To answer the question: some amount of socialism may be of use in a sort of "emotional safety blanket" kind of way, but in a purely practical sense, I think it hurts, rather than helps, the poor and middle classes over time.
-Taric