That is a really poor argument and can be debunked with some simple thought modeling. Imagine a system where returns on capital are higher than labor, and there are a relatively small number of people with large amounts of capital and no 'socialist' policies in place to attempt to interrupt the capital flow. After a period of time, assuming everyone is working and investing if they have capital to spare, would the income be more or less evenly distributed? This result would occur outside of socialist policies so it's very doubtful they are the cause.